Light diffuser with colored variable diffusion

ABSTRACT

The invention provides a light diffuser comprising a macro diffusion efficiency variation wherein at least part of the diffuser is colored. The invention also provides light diffuser comprising a macro diffusion efficiency variation wherein at least part of the diffuser is colored for rear projection displays, back-lighted imaging media, and a liquid crystal display component and device. The invention further provides a process for preparing such a diffuser.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is one of a group of five applications co-filedunder Attorney Docket Nos. 83948/AEK, 84008/AEK, 84301/AEK, 84393/AEK,and 84407/AEK the contents of which are incorporated herein byreference.

FIELD OF THE INVENTION

[0002] The invention relates to a colored variable diffuser for specularlight. In a preferred form, the invention relates to a colored variableback light diffuser for rear projection liquid crystal display devices.

BACKGROUND OF THE INVENTION

[0003] Optical structures that scatter or diffuse light generallyfunction in one of two ways: (a) as a surface diffuser utilizing surfaceroughness to refract or scatter light in a number of directions; or (b)as a bulk diffuser having flat surfaces and embedded light-scatteringelements.

[0004] A diffuser of the former kind is normally utilized with its roughsurface exposed to air, affording the largest possible difference inindex of refraction between the material of the diffuser and thesurrounding medium and, consequently, the largest angular spread forincident light. However, some prior art light diffusers of this typesuffer from a major drawback: the need for air contact. The requirementthat the rough surface must be in contact with air to operate properlymay result in lower efficiency. If the input and output surfaces of thediffuser are both embedded inside another material, such as an adhesivefor example, the light-dispersing ability of the diffuser may be reducedto an undesirable level.

[0005] In one version of the second type of diffuser, the bulk diffuser,small particles or spheres of a second refractive index are embeddedwithin the primary material of the diffuser. In another version of thebulk diffuser, the refractive index of the material of the diffuservaries across the diffuser body, thus causing light passing through thematerial to be refracted or scattered at different points. Bulkdiffusers also present some practical problems. If a high angular outputdistribution is sought, the diffuser will be generally thicker than asurface diffuser having the same optical scattering power. If howeverthe bulk diffuser is made thin, a desirable property for mostapplications, the scattering ability of the diffuser may be too low.

[0006] Despite the foregoing difficulties, there are applications wherea surface diffuser may be desirable, where the bulk type of diffuserwould not be appropriate. For example, the surface diffuser can beapplied to an existing film or substrate thus eliminating the need for aseparate film. In the case of light management in a LCD, this increasesefficiency by removing an interface (which causes reflection and lostlight).

[0007] It is desirable to have the amount of diffusion vary across thediffusion film, whether a bulk or surface diffuser, to compensate foruneven brightness across a backlit display. A diffuser film with uniformdiffusion across the film must have the diffusion efficiency to diffusethe most intense, specular areas of the display across the entirediffuser. These diffusers tend to need high levels of diffusionefficiency causing lower percentages total transmission across theentire film. With a diffuser with variable diffusion efficiency, theareas of high specular light could be diffused more than areas of lessspecular light. The result would be a display that had even diffuselight across it while having a higher overall transmission valuecompared to the uniform diffusion film.

[0008] The colored variable diffusion film evens out the color andillumination of the backlight across the display using a gradient incolor tone, color density, and diffusivity. For a backlight with thelight source in the center of the display, the percent total lighttransmission would increase and diffuse light transmission woulddecrease from the center of the roll to the edge of the roll. The filmwould be more diffuse and less transparent in the center of the displaywhere the light is located, to compensate for the light intensity of thelight bulb. Towards the edge of the film and display, away from thelight source, more light passes through the film and the light isdiffused less to create an even light intensity across the entiredisplay. Selective coloration of the variable diffuser creates an evencolor tone across the display by using higher density color close to thelight source and lower color density away from the light to create aneven color across the display. Using colored variable diffusers evenillumination and color across the display can be achieved.

[0009] In U.S. Pat. No. 6,270,697 (Meyers et al.), blur films are usedto transmit infrared energy of a specific waveband using a repeatingpattern of peak-and-valley features. While this does diffuse visiblelight, the periodic nature of the features is unacceptable for abacklight LC device because the pattern can be seen through the displaydevice.

[0010] U.S. Pat. No. 6,266,476 (Shie et al.) discloses a microstructureon the surface of a polymer sheet for the diffusion of light. Themicrostructures are created by molding Fresnel lenses on the surface ofa substrate to control the direction of light output from a light sourceso as to shape the light output into a desired distribution, pattern orenvelope. The materials disclosed in U.S. Pat. No. 6,266,476 shape andcollimate light, and therefore are not efficient diffusers of lightparticularly for liquid crystal display devices.

[0011] It is known to produce a base having a resin coated on onesurface thereof with the resin having a surface texture. This kind ofbase is made by a thermoplastic embossing process in which raw(uncoated) base is coated with a molten resin, such as polyethylene. Thebase with the molten resin thereon is brought into contact with a chillroller having a surface pattern. Chilled water is pumped through theroller to extract heat from the resin, causing it to solidify and adhereto the base. During this process the surface texture on the chillroller's surface is embossed into the resin coated base. Thus, thesurface pattern on the chill roller is critical to the surface producedin the resin on the coated base.

[0012] One known prior process for preparing chill rollers involvescreating a main surface pattern using a mechanical engraving process.The engraving process has many limitations including misalignmentcausing tool lines in the surface, high price, and lengthy processing.Accordingly, it is desirable to not use mechanical engraving tomanufacture chill rollers.

[0013] In U.S. Pat. No. 6,381,068 (Harada et al.) the diffusing elementmay be a bulk diffuser including a transparent base material of and atleast one light-diffusing material, such as a pigment and/or beads,dispersed in the transparent base material. The pigments used mayinclude a white pigment (for example, titanium oxide) and may alsoinclude one or more colored pigments. The pigments in this invention areonly used with a uniform diffuser and not a variable diffuser.Furthermore, the colored pigments must be a single color tone anddensity across the display. The colored variable diffuser can tailor thecolor and diffusion properties of the film as a function of location onthe film with varying colors and densities across the film.

[0014] In U.S. Pat. No. 6,266,476 (Shie et al.) a monolithic elementhaving a substrate body and a macro-optical characteristic produced bysurface micro-structures. These micro-structures can be non-uniformacross the lens to minimize certain lens aberrations. These non-uniformmicro-structures reduce lens aberrations, but are not able tosignificantly alter the macro-optical characteristics of the opticalbody. The diffusing structures, in this invention, vary as to change themacro diffusion efficiency across the diffusion film. The diffusionelements can vary changing the diffusion characteristics of thediffusion area from diffusing most of the light to letting light passspecularly which micro-structures are unable to do.

[0015] U.S. Pat. No. 6,285,001 (Fleming et al) relates to an exposureprocess using excimer laser ablation of substrates to improve theuniformity of repeating microstructures on an ablated substrate or tocreate three-dimensional microstructures on an ablated substrate. Thismethod is difficult to apply to create a master chill roll tomanufacture complex random three-dimensional structures and is also costprohibitive.

[0016] In U.S. Pat. No. 6,124,974 (Burger) the substrates are made withlithographic processes. This lithography process is repeated forsuccessive photomasks to generate a three-dimensional relief structurecorresponding to the desired lenslet. This procedure to form a master tocreate three-dimensional features into a plastic film is time consumingand cost prohibitive.

[0017] U.S. Pat. No. 6,093,521 describes a photographic membercomprising at least one photosensitive silver halide layer on the top ofsaid member and at least one photosensitive silver halide layer on thebottom of said member, a polymer sheet comprising at least one layer ofvoided polyester polymer and at least one layer comprising nonvoidedpolyester polymer, wherein the imaging member has a percent transmissionof between 38 and 42%. While the voided layer described in U.S. Pat. No.6,093,521 does diffuse back illumination utilized in prior art lightboxes used to illuminate static images, the percent transmission between38 and 42% would not allow a enough light to reach an observers eye fora liquid crystal display. Typically, for liquid crystal display devices,back light diffusers must be capable of transmitting at least 65% andpreferably at least 80% of the light incident on the diffuser.

[0018] In U.S. Pat. No. 6,030,756 (Bourdelais et al), a photographicelement comprises a transparent polymer sheet, at least one layer ofbiaxially oriented polyolefin sheet and at least one image layer,wherein the polymer sheet has a stiffness of between 20 and 100millinewtons, the biaxially oriented polyolefin sheet has a spectraltransmission between 35% and 90%, and the biaxially oriented polyolefinsheet has a reflection density less than 65%. While the photographicelement in U.S. Pat. No. 6,030,756 does separate the front silver halidefrom the back silver halide image, the voided polyolefin layer woulddiffuse too much light creating a dark liquid crystal display image.Further, the addition of white pigment to the sheet causes unacceptablescattering of the back light.

[0019] In U.S. Pat. No. 5,223,383 photographic elements containingreflective or diffusely transmissive supports are disclosed. While thematerials and methods disclosed in this patent are suitable forreflective photographic products, the % light energy transmission (lessthan 40%) is not suitable for liquid crystal display as % lighttransmission less than 40% would unacceptable reduce the brightness ofthe LC device.

[0020] In U.S. Pat. No. 4,912,333, X-ray intensifying screens utilizemicrovoided polymer layers to create reflective lenslets forimprovements in imaging speed and sharpness. While the materialsdisclosed in U.S. Pat. No. 4,912,333 are transmissive for X-ray energy,the materials have a very low visible light energy transmission that isunacceptable for LC devices.

[0021] In U.S. Pat. No. 6,177,153, oriented polymer film containingpores for expanding the viewing angle of light in a liquid crystaldevice is disclosed. The pores in U.S. Pat. No. 6,177,153 are created bystress fracturing solvent cast polymers during a secondary orientation.The aspect ratio of these materials, while shaping incident light,expanding the viewing angle, do not provide uniform diffusion of lightand would cause uneven lighting of a liquid crystal formed image.Further, the disclosed method for creating voids results in void sizeand void distribution that would not allow for optimization of lightdiffusion and light transmission. In example 1 of this patent, thereported 90% transmission includes wavelengths between 400 and 1500 nmintegrating the visible and invisible wavelengths, but the transmissionat 500 nm is less that 30% of the incident light. Such values areunacceptable for any diffusion film useful for image display, such as aliquid crystal display.

PROBLEM TO BE SOLVED BY THE INVENTION

[0022] There remains a need for an improved provide colored lighttransmission while simultaneously diffusing specular light sources.

SUMMARY OF THE INVENTION

[0023] The invention provides a light diffuser comprising a macrodiffusion efficiency variation wherein at least part of the diffuser iscolored. The invention also provides light diffuser comprising a macrodiffusion efficiency variation wherein at least part of the diffuser iscolored for rear projection displays, back-lighted imaging media, and aliquid crystal display component and device. The invention provides aprocess comprising color transfer.

ADVANTAGEOUS EFFECT OF THE INVENTION

[0024] The invention provides colored transmission for a back litdisplay while simultaneously diffusing specular light sources. It alsoprovides colored variable diffusers for display media.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025]FIG. 1 illustrates a cross section of a colored variable diffusioncomplex lens formed on a base material suitable for use in a liquidcrystal display device.

[0026]FIG. 2 illustrates a liquid crystal display device with a coloredvariable diffusion complex lens polymer light diffuser.

DETAILED DESCRIPTION OF THE INVENTION

[0027] The invention has numerous advantages over prior practices in theart. The prior art diffusion screen, uniform across the film surface,could not tailor the light transmission, diffusion, and color as afunction of position on the film. The colored variable diffusion filmcan be designed to the light source and the display. The coloredvariable diffusion film evens out the color and illumination of thebacklight across the display using a gradient in color tone, colordensity, and diffusivity. For a display with the light source in thecenter of the display, the percent total light transmission wouldincrease and diffuse light transmission would decrease from the centerof the roll to the edge of the roll. The film would be more diffuse andless transparent in the center of the display where the light islocated, to compensate for the light intensity of the light bulb.Towards the edge of the film and display, away from the light source,more light passes through the film and the light is diffused less tocreate an even light intensity across the entire display. Selectivecoloration of the variable diffuser creates an even color tone acrossthe display by using higher density color close to the light source andlower color density away from the light to create an even color acrossthe display. Using colored variable diffusers even illumination andcolor across the display can be achieved.

[0028] A high transmission rate for light diffusers is particularlyimportant for liquid crystal display devices as a high transmissionvalue allows the liquid crystal display to be brighter or holding thelevel of brightness the same, allows for the power consumption for theback light to be reduces therefore extending the lifetime of batterypowered liquid crystal devices that are common for note book computers.The invention can be easily changed to achieve the desired diffusion,diffusion variation, and light transmission requirements for many liquidcrystal devices thus allowing the invention materials to be responsiveto the rapidly changing product requirements in the liquid crystaldisplay market.

[0029] A voided polymer diffuser and a complex lens surface diffuser canbe easily altered in both pre and post-manufacturing processes toachieve the desired variable diffusion, light transmission, and colorrequirements for many liquid crystal. These technologies allow theinvention materials to be responsive to the rapidly changing productrequirements in the liquid crystal display market.

[0030] Further, the light diffuser with efficiency variation can createpatterns, text, and pictures by diffusing light selectively to createareas of diffusion, less diffusion, and no diffusion (specular). Thecolored variable diffuser can display text, shapes, and images invarying amounts of diffusion or specular areas and different colorssurrounded by diffuse regions. These colored variable diffusers can beused in displays and as overheads. As overheads the colored variablediffuser has added utility. In an unexpected result, when the coloredvariable diffuser was placed on an overhead projector, the diffuse areaswere dark, and the specular areas were bright. This occurred becausewhen the light from the light source in the overhead projector hit thediffuse areas of the diffuser sheet, the light was diffused and thefocusing lens did not collect the light and the image projected wasdark. The specular areas transmitted specular light producing brightareas on the display. Colored variable diffusion sheets, with thereability to produce colored text, shapes, and images with diffuse andspecular areas, can be used as project materials to improve the contrastin the projected sheet allowing the display to be more easily read in abright room and producing for an unusual display effect.

[0031] The diffusion film of the present invention can be produced byusing a conventional film-manufacturing facility in high productivityusing roll to roll manufacturing processes. These and other advantageswill be apparent from the detailed description below.

[0032] Color can be applied by any method, for example inkjet, flexoprinting, gravure printing, screen printing, electrophotography, andthermal dye sublimation. The coloration techniques can apply heat andpressure to change the characteristics of the diffusion film, or notapply heat and pressure and apply to an diffusion film with variablediffusion efficency.

[0033] The term “LCD” means any rear projection display device thatutilizes liquid crystals to form the image. The term “diffuser” meansany material that is able to diffuse specular light (light with aprimary direction) to a diffuse light (light with random lightdirection). “Specular” means light with a primary differection and ahaze value of 15% or less. The term “light” means visible light. Theterm “diffuse light transmission” means the percent diffuselytransmitted light at 500 nm as compared to the total amount of light at500 nm of the light source. The term “total light transmission” meanspercentage light transmitted through the sample at 500 nm as compared tothe total amount of light at 500 nm of the light source. This includesboth spectral and diffuse transmission of light. The term “diffusionefficiency” means the ratio of % diffuse transmitted light at 500 nm to% total transmitted light at 500 nm multiplied by a factor of 100. Theterm “polymeric film” means a film comprising polymers. The term“polymer” means homo- and co-polymers. The term “average”, with respectto lens size and frequency, means the arithmetic mean over the entirefilm surface area. “Diffuse areas” means areas in a film where the hazeof the light transmitted is more than 15%. “Specular areas” means areasin a film where the haze of the light transmitted is 15% or less.

[0034] “Transparent” means a film with total light transmission of 50%or greater at 500 nm. “In any direction”, with respect to lensletarrangement on a film, means any direction in the x and y plane. Theterm “pattern” means any predetermined arrangement whether regular orrandom.

[0035] “Macro diffusion efficiency variation” means a diffusionefficiency variation that is greater than 5% over an in plane distanceof at least 2 cm. An optical gradient is a change in optical propertiessuch as transmission, reflection, light direction as a function ofdistance from a stating point. Useful examples of an optical gradientinclude a light transmission gradient, a light diffusion gradient andlight adsorption gradient. “Gradient”, in reference to diffusion, meansthe increasing or decreasing of diffusion efficiency relative todistance from a starting point. “Colored macro diffusion efficiencyvariation” and “colored variable diffusers” means a diffuser that has amacro diffusion efficiency variation and at least part of the diffuseris colored. “Color” and “chromatic” mean light in the visiblewavelengths (approximately 400-750 nanometers) that are seen by theviewer as having coloration.

[0036] Better control and management of the back light are drivingtechnological advances for liquid crystal displays (LCD). LCD screensand other electronic soft display media are back lit primarily withspecular (highly directional) fluorescent tubes. Diffusion films areused to distribute the light evenly across the entire display area andchange the light from specular to diffuse. Light exiting the liquidcrystal section of the display stack leaves as a narrow column and mustbe redispersed. Diffusers are used in this section of the display toselectively spread the light out horizontally for an enhanced viewingangle.

[0037] Diffusion is achieved by light scattering as it passes thoughmaterials with varying indexes of refraction. This scattering produces adiffusing medium for light energy. There is an inverse relationshipbetween transmittance of light and diffusion and the optimum combinationof these two parameters is desired for each application.

[0038] The back diffuser is placed directly in front of the light sourceand is used to even out the light throughout the display by alteringspecular light into diffuse light. Prior art methods for diffusing LCDback light include layering polymer films with different indexes ofrefraction, microvoided polymer film, micro surface structures, orcoating the film with matte resins or beads. The role of the frontdiffuser is to broaden the light coming out of the liquid crystal (LC)with directional selectivity. The light is compressed into a tight beamto enter the LC for highest efficiency and when it exits it comes out asa narrow column of light. The diffuser uses optical structures to spreadthe light selectively. Most companies form elliptical micro-lens toselectively stretch the light along one axis. Elliptically shapedpolymers in a polymer matrix and surface micro-lenses formed by chemicalor physical means also achieve this directionality.

[0039] In one embodiment of the invention, the diffusion film has atextured surface on at least one side, in the form of a plurality ofrandom microlenses, or lenslets. The term “lenslet” means a small lens,but for the purposes of the present discussion, the terms lens andlenslet may be taken to be the same. The lenslets overlap to formcomplex lenses. “Complex lenses” means a major lens having on thesurface thereof multiple minor lenses. “Major lenses” mean largerlenslets that the minor lenses are formed randomly on top of “Minorlenses” mean lenses smaller than the major lenses that are formed on themajor lenses. The plurality of lenses of all different sizes and shapesare formed on top of one another to create a complex lens featureresembling a cauliflower. The lenslets and complex lenses formed by thelenslets can be concave into the base or convex out of the base. Theterm “concave” means curved like the surface of a sphere with theexterior surface of the sphere closest to the surface of the film. Theterm “convex” means curved like the surface of a sphere with theinterior surface of the sphere closest to the surface of the film. Theterm “top surface” means the surface of the film farther from the lightsource. The term “bottom surface” means the surface of the film closerto the light source.

[0040] The term “polymer” means homo- and co-polymers. The termmicrobead means polymeric spheres typically synthesized using thelimited coalescence process. These microbead spheres can range in sizefrom 0.2 to 30 micrometers. They are preferably in the range of 0.5 to5.0 micrometers. The term microvoids means pores formed in an orientedpolymeric film during stretching. These pores are initiated by inorganicparticles, organic particles, or microbeads. The size of these voids isdetermined by the size of the particle or microbeads used to initiatethe void and by the stretch ratio used to stretch the oriented polymericfilm. The pores can range from 0.6 to 150 μms in machine and crossmachine directions of the film. They can range from 0.2 to 30micrometers in height. Preferably the machine and cross machinedirection pore size is in the range of 1.5 to 25 micrometers. Preferablythe height of the pores is in the range of 0.5 to 5.0 micrometers. Theterm substantially circular means indicates a geometrical shape wherethe major axis is no more than two times the minor axis.

[0041] It has been shown that a colored variable diffuser film cantailor the light source in diffusivity and coloration with respect tolocation on the film. It has been shown that the most efficient coloreddiffuser films would have higher diffusion values and color density nearthe light sources to destruct the light source shape and perform colorcorrection and less diffusion and color density away from the lightsource. Having a light diffuser with colored macro diffusion efficiencyenables the diffuser to tailor the diffusion, transmission, and colorproperties as a function of location on the diffuser film. In a back-litdisplay, when the diffusion film is tailored to the needs of thebacklight, higher light transmission and diffusion efficiency and moreeven color tone can be achieved. It has been shown that selectivecoloration of the variable diffuser creates an even color tone acrossthe display. For example, a display might have a red tint to it and thedesire is to have a neutral display. The diffuser for the light sourcewould nee to have a cyan component to it, higher in density close to thelight source and lower in density away from the light to create an evencolor across the display. Using colored variable diffusers displays canbe fabricated with even illumination and color across the display.

[0042] Further, a light diffuser with colored macro efficiency variationcan eliminate the need for edge printing on the diffusion film and dotprinting on the acrylic light guide. These printing devices were toguide the light through back light of an LCD to be used more efficientlyby the liquid crystal and to “hide” the light sources from the viewer.Further, the light diffuser with efficiency variation can createpatterns, text, and pictures by diffusing light selectively to createareas of diffusion, less diffusion, and no diffusion (specular). Thiscan create differentiated backlit media such as backlit display,greeting cards, and printed media.

[0043] Preferably, the colored light diffuser has a color with at leastthe density of 0.2. A color density of less than 0.1 could be caused bycoloration in the materials and could vary due to manufacturingprocesses. A color density of 0.2 is enough density to be used indisplay media and as color correction for light sources.

[0044] It is preferred that the specular areas of the macro efficiencyvariation are colored. This creates text, graphics, shapes, and imagesin specular colored areas surrounded by diffuse regions creating mediathat can become display media or overhead projection films, for example.Preferably, the diffuse areas of the macro efficiency variation arecolored because the film can color light transmitted diffusely. This canbe used to color correct lighting for artwork or anywhere that thevariable diffuser would need coloration. Furthermore, the color tone anddensity can change over the diffuse regions of the film. In anotherembodiment of the invention, diffusion gradient areas of the macroefficiency variation are colored. In this embodiment, the gradient fromspecular to diffuse regions of the film are colored with a uniform orvarying color tone and density. This creates unique display and lightingeffects and can be used in the backlight assemblies of LC displays forcolor tone and illumination evening.

[0045] The colored macro diffusion efficiency variation comprising dyebased colorants is preferred. Dye based colorants are preferred becauseof the ease of application to the variable diffuser films. They arerelatively inexpensive and have a large color gamut. Dye can be appliedto the diffuse film, for example, by inkjet, thermal dye sublimation,and screen printing. A dye is a colorant, which is dissolved in thecarrier medium. Any dye may be used in this invention. Preferably, anyanionic, water-soluble dye may be used such as a dye having an anionicgroup, e.g., a sulfo group or a carboxylic group. The anionic,water-soluble dye may be any acid dye, direct dye or reactive dye listedin the COLOR INDEX but is not limited thereto. Metallized andnon-metallized azo dyes may also be used as disclosed in U.S. Pat. No.5,482,545, the disclosure of which is incorporated herein by reference.Other dyes which may be used are found in EP 802246-A1 and JP09/202,043, the disclosures of which are incorporated herein byreference. A Mixture of dyes may also be used.

[0046] The colored macro diffusion efficiency variation comprisingpigment based colorants is preferred. Pigment based colorants arepreferred because of the ease of application to the variable diffuserfilms and for the image stability of the pigments. Pigments can beapplied to the diffuse film, for example, by inkjet, thermal dyesublimation, and screen printing. In pigment-based inks, the colorantexists as discrete particles. These pigment particles are usuallytreated with addenda known as dispersants or stabilizers which serve tokeep the pigment particles from agglomerating and settling out of thecarrier. Water-based pigmented inks are prepared by incorporating thepigment in the continuous water phase by a milling and dispersingprocess. In the present invention, any of the known organic pigments canbe used. Pigments can be selected from those disclosed, for example, inU.S. Pat. Nos. 5,026,427; 5,085,698; 5,141,556; 5,160,370 and 5,169,436,the disclosures of which are hereby incorporated by reference. Thepigment can be a colored pigment, or a black colored pigment, such ascarbon black. The exact choice of pigment, or mixture of pigments, willdepend upon the specific color reproduction and image stabilityrequirements of the printer and application.

[0047] Preferably, the colored light diffuser comprises fluorescentmaterials. An optical brightener is substantially colorless,fluorescent, organic compound that absorbs ultraviolet light and emitsit as visible blue light.

[0048] Examples include but are not limited to derivatives of4,4′-diaminostilbene-2,2′-disulfonic acid, coumarin derivatives such as4-methyl-7-diethylaminocoumarin, 1-4-Bis (O-Cyanostyryl) Benzol and2-Amino-4-Methyl Phenol. Because the ultraviolet source for atransmission display material is on the opposite side of the LC, theultraviolet light intensity is not reduced by ultraviolet filters commonto polarizers. The result is less optical brightener is required toachieve the desired background color. This can create coloration in thevariable diffuser.

[0049] Preferably, the macro diffusion efficiency variation correspondsto a color wavelength band of 10 to 70 nanometers wide. This creates acolored variable diffuser with a very specific narrow color band. Havings narrow color band can very selectively transmit or block light ofvarying wavelengths tailoring the light. It has been shown thatproducing narrow color band of light creates a more “pure” color oflight and is more efficient for use in liquid crystal display colormatrixes because the red, green, and blue color filters only transmitspecific wavelengths of light.

[0050] The light diffuser where the colored macro diffusion efficiencyvariation comprises text is preferred. In another embodiment of theinvention, the colored macro diffusion efficiency variation comprisinggraphics are preferred. Preferably, the colored macro diffusionefficiency variation comprises images. The colored variable lightdiffuser can have areas of text, graphics, and images in selectedamounts of diffusion. For example, areas of diffuse text can besurrounded by specular colored areas or an image can be formed where allareas of white of the image are diffuse and the colored areas of theimage are semi-diffuse to specular colored. This creates unique displaymedia such as backlit displays, display media, overheads, and greetingcards.

[0051] The light diffuser comprising a colored element is preferred.This colored element can produce colored transmissions or correct thecoloration of the light source. Or example, if a display requiredneutral colored light and the light source used was blue in color, ayellow colored element could be added to the diffuser so that thetransmission of the diffuser would be neutral and more suited to thedisplay. “Colored element” means any colored material, a substance, suchas a dye, pigment, or paint that imparts a hue.

[0052] A light diffuser wherein the macro diffusion efficiency variationcomprises chromatic transmission is preferred. To obtain chromatictransmission, different wavelengths that compose white light areaffected differently by refraction. For example, the red radiation (withlonger wavelengths) are less deviated while the blue or violet radiationare more deviated from their initial direction and this creates achromatic transmission.

[0053] The light diffuser wherein the chromatic transmission comprisesyellow light at 570 to 620 nm is preferred. In another embodiment of theinvention, the chromatic transmission comprises magenta light at 630 to690 nm and 425 to 480 nm is preferred. Preferably, the chromatictransmission comprises cyan light at 480 to 520 nm. In anotherembodiment of the invention, the chromatic transmission comprises redlight at 630 to 690 nm. The preferred diffuse tranmission comprisesgreen light at 525 to 590 nm. For another application, the preferreddiffuse transmission comprises blue light at 425 to 480 nm. The desiredchromatic transmission color depends on the application and use.

[0054] A light diffuser wherein the diffusion efficiency varies morethan 5 percent in two different locations of the diffuser is preferred.A diffusion efficiency that varies less than 3 percent could be causedby variations in the diffusion film caused by manufacturing processvariations. Most preferred is a diffusion efficiency that varies morethan 50 percent in two different locations of the diffuser. It has beenshown that over 50 percent variation in two different locations of thediffuser film produces a film that can be tailored to diffusing needs ofthe backlight.

[0055] A light diffuser wherein the diffusion efficiency variationcomprises a gradient is preferred. Have a gradient allows for the smoothtransition from one diffusion efficiency to another diffusionefficiency. For example, in a liquid crystal display, it is desirable tohave more diffusion by the light source because the light is moreintense and specular in that region, however, it is not desirable forthe viewer to see the transition in the diffusion film. A gradientallows that transition to be undetectable by the viewer. The diffusionefficiency can change by the following mathematical variations, forexample:

Diffusion efficiency=e ^(1/distance) or e ^(−1/distance)

Diffusion efficiency=1/distance or −1/distance

Diffusion efficiency=distance*x or −distance*x (where x is a realnumber)

[0056] Each specific light diffusing application determines the amountof variation needed and the rate at which diffusion efficiency changeswith respect to distance.

[0057] The diffusion film is tailored to the backlight and the lightsource to be diffused. Typically, to produce an evenly lit display,there need to be more diffusion near the light source and less furtheraway from the light source. Where the light source is positioned inrelation to the display determines what variable diffuser is needed. Thepreferred light diffuser that is rectangle is shape has a diffusionefficiency variation along a diagonal of the rectangle. This would bedesirable to compensate for a lighting variation on a diagonal of arectangle. In another embodiment of the invention, the preferred lightdiffuser that is rectangular in shape has a diffusion efficiencyvariation along the width or height of the rectangle. For anotherapplication, the preferred light diffuser has a diffusion efficiencyvariation from the center to the perimeter of the diffusion film.Preferably, the light diffuser has a diffusion efficiency variationalong the perimeter of the diffusion film. The preferred light diffuserhas a diffusion efficiency variation such that the iso-efficiencyexhibits an elliptical pattern. The preferred light diffuser has adiffusion efficiency variation having a pattern. The variable diffusionfilm can take on any of these variations based on the backlight anddisplay configuration.

[0058] For example, prior art light diffusers for liquid crystal displaydevices utilize edge or perimeter printing of the light diffuser todirect light away from the edges of the display were the light istypically absorbed into the LCD frame. Light adsorbed into the LCD frameis lost light energy in that absorbed illumination light energy can notbe used to illuminate the LC image. Prior art diffusers for LCD devicesare typically printed with white or silver, reflecting dots around theperimeter that provide specular reflection of perimeter light so thatsome of the perimeter light can be “recycled” by the illuminationcomponents away from the perimeter. While the printing of whitereflective dots does reduce the amount of absorbed light energy by theLCD frame, perimeter printing is expensive in that it required anadditional printing operation. Further, the perimeter printing of thelight diffuser has been generally shown to reduce edge absorption by30%. Using less diffuse region (a more specular region) around theperimeter of the diffusion film, more of the light would be directedstraight out of the backlight and into usable space on the displayinstead of being directed towards the edge of the display and beinglost.

[0059] Preferably, the light diffuser has a diffusion efficiencyvariation having a specular component. Using pre or post-manufacturingprocesses, the diffusion film can be selectively “turned on” or “turnedoff” meaning the areas can be diffuse, or specular. The edge printingtypically done on back diffusers for LCD can be replaced by creating aspecular edge around the film, thus directing the light specularlyinstead of reflecting it thus creating a brighter display. The specularareas of the film can also form patterns and text. Films with areas ofspecular and diffuse light transmittance can also be used as overheadprojection films where the diffuse areas show up as darker areas on thedisplay and the specular areas show up as bright areas on the display.The light diffuser where specular areas of the film are colored arepreferred. This can create colored areas of specular patterns, text,images, and graphics. Films with areas of colored specular andnon-colored diffuse light transmittance can be used as overheadprojection films where the diffuse areas show up as darker areas on theprojection display and the specular areas show up as bright coloredareas on the display. This creates a colored projection film that hasincreased contrast to be viewed in room light conditions without theneed to turn the ambient light down.

[0060] The preferred light diffuser has a diffusion efficiency variationof at least 10% less diffusion efficiency on the edges of the diffusionfilm than the center of the film. At the edge of a liquid crystaldisplay, some of the light that is diffused is lost as it is deflectedaway and off the device. By making the edge of the display less diffusethan the center, less of the light is lost off of the display and theresult is a brighter display. This can reduce or eliminate the need foredge printing on the diffusion film.

[0061] A light diffusion film having a top and bottom surface comprisinga plurality of convex or concave complex lenses on the surface of thebase is preferred. Curved concave and convex polymer lenses have beenshown to provide very efficient diffusion of light. Further, the polymerlenses of the invention are transparent, allowing a high transmission oflight allowing the brightness of LC displays to emit more light.Further, the complex lenses can be altered in design or a postprocessing method to achieve a macro diffusion efficiency variation.

[0062] One embodiment of the present invention could be likened to themoon's cratered surface. Asteroids that hit the moon form craters apartfrom other craters, that overlap a piece of another crater, that formwithin another crater, or that engulf another crater. As more cratersare carved, the surface of the moon becomes a complexity of depressionslike the complexity of lenses formed in the base.

[0063] The surface of each lenslet is a locally spherical segment, whichacts as a miniature lens to alter the ray path of energy passing throughthe lens. The shape of each lenslet is “semi-spherical” meaning that thesurface of each lenslet is a sector of a sphere, but not necessarily ahemisphere. Its curved surface has a radius of curvature as measuredrelative to a first axis (x) parallel to the base and a radius ofcurvature relative to second axis (y) parallel to the base andorthogonal to the first axis (x). The lenses in an array film need nothave equal dimensions in the x and y directions. The dimensions of thelenses, for example length in the x or y direction, are generallysignificantly smaller than a length or width of the film.“Height/Diameter ratio” means the ratio of the height of the complexlens to the diameter of the complex lens. “Diameter” means the largestdimension of the complex lenses in the x and y plane. The value of theheight/diameter ratio is one of the main causes of the amount of lightspreading, or diffusion that each complex lens creates. A smallheight/diameter ratio indicates that the diameter is much greater thanthe height of the lens creating a flatter, wider complex lens. A largerheight/diameter value indicates a taller, skinner complex lens. Thecomplex lenses may differ in size, shape, off-set from optical axis, andfocal length.

[0064] The curvature, depth, size, spacing, materials of construction(which determines the basic refractive indices of the polymer film andthe substrate), and positioning of the lenslets determine the degree ofdiffusion, and these parameters are established during manufactureaccording to the invention.

[0065] The divergence of light through the lens may be termed“asymmetric”, which means that the divergence in the horizontaldirection is different from the divergence in the vertical direction.The divergence curve is asymmetric, meaning that the direction of thepeak light transmission is not along the direction θ=0°, but is in adirection non-normal to the surface. There are at least three approachesavailable for making the light disperse asymmetrically from a lensletdiffusion film, namely, changing the dimension of the lenses in onedirection relative to an orthogonal direction, off-setting the opticalaxis of the lens from the center of the lens, and using an astigmaticlens.

[0066] The result of using a diffusion film having lenses whose opticalaxes are off-set from the center of the respective lenses results indispersing light from the film in an asymmetric manner. It will beappreciated, however, that the lens surface may be formed so that theoptical axis is off-set from the center of the lens in both the x and ydirections.

[0067] The lenslet structure can be manufactured on the opposite sidesof the substrate. The lenslet structures on either side of the supportcan vary in curvature, depth, size, spacing, and positioning of thelenslets.

[0068] The concave or complex lenses on the surface of the polymer filmare preferably randomly placed. Random placement of lenses increases thediffusion efficiency of the invention materials. Further, by avoiding aconcave or convex placement of lenses that is ordered, undesirableoptical interference patterns are avoided.

[0069] In an embodiment of the invention, the concave or convex lensesare located on both sides of the transparent polymer sheet. By placingthe lenses on both sides of the transparent sheet, more efficient lightdiffusion is observed compared to the lenses of the invention on oneside. Further, the placement of the lenses on both sides of thetransparent sheet increases the focal length of the lenses furthest fromthe brightness enhancement film in a LC display device. Further, thediffusion efficiency and diffusion variation can vary from one side ofthe diffusion film to the other side. This enables the one diffusionsheet to have two different macro diffusion variations or gradients (oneon each side) achieving a more customized film. For example, the side ofthe diffusion film closer to the light source can have a diffusiongradient for more course diffusion and the opposite side (away from thelight source) can have more fine diffusion structures with more complexpatterns and gradients' to achieve the overall variable diffuserdesired.

[0070] Preferably, the concave or convex lenses have an averagefrequency in any direction of from 5 to 250 complex lenses/mm. When afilm has an average of 285 complex lenses/mm, creates the width of thelenses approach the wavelength of light. The lenses will impart a colorto the light passing through the lenses and change the color temperatureof the display. Less than 4 lenses/mm Creates lenses that are too largeand therefore diffuse the light less efficiently. Concave or convexlenses with an average frequency in any direction of between 22 and 66complex lenses/mm are more preferred. It has been shown that an averagefrequency of between 22 and 66 complex lenses provide efficient lightdiffusion and can be efficiently manufactured utilizing cast coatedpolymer against a randomly patterned roll.

[0071] The light diffuser has concave or convex lenses at an averagewidth between 3 and 60 microns in the x and y direction. When lenseshave sizes below 1 micron the lenses impart a color shift in the lightpassing through because the lenses dimensions are on the order of thewavelength of light. When the lenses have an average width in the x or ydirection of more than 68 microns, the lenses is too large to diffusethe light efficiently. More preferred, the concave or convex lenses atan average width between 15 and 40 microns in the x and y direction.This size lenses has been shown to create the most efficient diffusion.

[0072] The concave or convex complex lenses comprising minor lenseswherein the width in the x and y direction of the smaller lenses ispreferably between 2 and 20 microns. When minor lenses have sizes below1 micron the lenses impart a color shift in the light passing throughbecause the lenses dimensions are on the order of the wavelength oflight. When the minor lenses have sizes above 25 microns, the diffusionefficiency is decreased because the complexity of the lenses is reduced.More preferred are the minor lenses having a width in the x and ydirection between 3 and 8 microns. This range has been shown to createthe most efficient diffusion.

[0073] The convex or concave lenses preferably have a height/diameterratio of from 0.03 to 1.0. A height/diameter ratio of less than 0.01(very wide and shallow lenses) limits diffusion because the lenses donot have enough curvature to efficiently spread the light. Aheight/diameter ratio of greater than 2.5 creates lenses where the anglebetween the side of the lenses and the substrate is large. This causesinternal reflection limiting the diffusion capability of the lenses.Most preferred is a height/diameter of the convex or concave lenses offrom 0.25 to 0.48. It has been found that the most efficient diffusionoccurs in this range.

[0074] The number of minor lenses per major lens is preferably from 2 to60. When a major lens has one or no minor lenses, its complexity isreduced and therefore it does not diffuse as efficiently. When a majorlens has more than 70 minor lens contained on it, the width of some ofthe minor lens approaches the wavelength of light and imparts a color tothe light transmitted. Most preferred are from 5 to 18 minor lenses permajor lens. This range has been shown to produce the most efficientdiffusion.

[0075] The preferred diffuse light transmission of the light is greaterthan 50%. Diffuser light transmissions less than 45% do not let asufficient quantity of light pass through the diffuser, thus making thediffuser inefficient. A more preferred diffuse light transmission of thelenslet film is at least 80 typically from 80 to 95%. An 80% diffusetransmission allows an LC device to have improved battery life andincreased screen brightness. The most preferred diffuse transmission ofthe base is at least 92%. A diffuse transmission of 92% allows diffusionof the back light-source and maximizes the brightness of the LC devicesignificant improving the image quality of an LC device for outdoor usewhere the LC screen must compete with natural sunlight.

[0076] Preferably, the concave or convex lenses are semi-sphericalmeaning that the surface of each lenslet is a sector of a sphere, butnot necessarily a hemisphere. This provides excellent even diffusionover the x-y plane. The semi-spherical shaped lenses scatter theincident light uniformly, ideal for a backlit display application wherethe display area needs to be lit uniformly. In another embodiment of theinvention, the concave or convex lenses are aspherical meaning thatwidth of the lenses differ in the x and y direction. This scatters lightselectively over the x-y plane. For example, a particular x-y aspectratio might produce an elliptical scattering pattern. This would beuseful in the front of a LC display, spreading the light more in thehorizontal direction than the vertical direction for increased viewingangle.

[0077] Preferably, the concave or convex complex lenses comprise anolefin repeating unit. Polyolefins are low in cost and high in lighttransmission. Further, polyolefin polymers are efficiently meltextrudable and therefore can be used to create light diffusers in rollform.

[0078] In another embodiment of the invention, the concave or convexcomplex lenses comprise a carbonate repeating unit. Polycarbonates havehigh optical transmission values that allows for high light transmissionand diffusion. High light transmission provides for a brighter LC devicethan diffusion materials that have low light transmission values.

[0079] In another embodiment of the invention, the concave or convexcomplex lenses comprise an ester repeating unit. Polyesters are low incost and have good strength and surface properties. Further, polyesterpolymer is dimensionally stable at temperatures between 80 and 200degrees C. and therefore can withstand the heat generated by displaylight sources.

[0080] Preferably, the polymeric support comprises an ester repeatingunit. Polyesters are low in cost and have good strength and surfaceproperties. Further, polyester polymer film is dimensionally stable overthe current range of temperatures encountered in enclosed displaydevices. Polyester polymer easily fractures allowing for die cutting ofdiffuser sheets for insertion into display devices.

[0081] In another embodiment of the invention, the polymeric supportcomprises a carbonate repeating unit. Polycarbonates have high opticaltransmission values compared to polyolefin polymers and therefore canimprove the brightness of display devices.

[0082] In another embodiment of the invention, the polymeric supportcomprises an olefin repeating unit. Polyolefins are low in cost and havegood strength and surface properties.

[0083] In another embodiment of the invention the polymeric supportcomprises a cellulose acetate. Tri acetyl cellulose has both highoptical transmission and low optical birefringence allowing the diffuserof the invention to both diffuse light and reduce unwanted opticalpatterns.

[0084] The thickness of the light diffuser preferably is not more than250 micrometers or more preferably from 12.5 to 100 micrometers. Currentdesign trends for LC devices are toward lighter and thinner devices. Byreducing the thickness of the light diffuser to not more than 250micrometers, the LC devices can be made lighter and thinner. Further, byreducing the thickness of the light diffuser, brightness of the LCdevice can be improved by reducing light transmission. The morepreferred thickness of the light diffuser is from 12.5 to 100micrometers which further allows the light diffuser to be convenientlycombined with a other optical materials in an LC device such asbrightness enhancement films. Further, by reducing the thickness of thelight diffuser, the materials content of the diffuser is reduced.

[0085] Since the thermoplastic light diffuser of the invention typicallyis used in combination with other optical web materials, a lightdiffuser with an elastic modulus greater than 500 MPa is preferred. Anelastic modulus greater than 500 MPa allows for the light diffuser to belaminated with a pressure sensitive adhesive for combination with otheroptical webs materials. Further, because the light diffuser ismechanically tough, the light diffuser is better able to with stand therigors of the assembly process compared to prior art cast diffusionfilms which are delicate and difficult to assemble. A light diffuserwith an impact resistance greater than 0.6 GPa is preferred. An impactresistance greater than 0.6 GPa allows the light diffuser to resistscratching and mechanical deformation that can cause unwanted unevendiffusion of the light causing “hot” spots in an LC device.

[0086] The light diffuser of the present invention can be produced byusing a conventional film-manufacturing facility in high productivity.The invention utilizes a voided thermal plastic layer containingmicrovoids. Microvoids of air in a polymer matrix are preferred and havebeen shown to be a very efficient diffuser of light compared to priorart diffuser materials which rely on surface roughness on a polymersheet to create light diffusion for LCD devices. The microvoided layerscontaining air have a large index of refraction difference between theair contained in the voids (n=1) and the polymer matrix (n=1.2 to 1.8).This large index of refraction difference provides excellent diffusionand high light transmission which allows the LCD image to be brighterand/or the power requirements for the light to be reduced thus extendingthe life of a battery. Further, the microvoided diffuser film can bealtered pre or post manufacturing to achieve the macro diffusionefficiency variation.

[0087] Since the microvoids of the invention are substantially air, theindex of refraction of the air containing voids is 1. An index ofrefraction difference between the air void and the thermoplastic matrixis preferably greater than 0.2. An index of refraction differencegreater than 0.2 has been shown to provide excellent diffusion of LCDback light sources and a index of refraction difference of greater than0.2 allows for bulk diffusion in a thin film which allows LCDmanufacturers to reduce the thickness of the LC screen. Thethermoplastic diffusion layer preferably contains at least 4 index ofrefraction changes greater than 0.2 in the vertical direction. Greaterthan 4 index of refraction changes have been shown to provide enoughdiffusion for most LC devices. 30 or more index of refractiondifferences in the vertical direction, while providing excellentdiffusion, significantly reduces the amount of transmitted light,significantly reducing the brightness of the LC device.

[0088] The light diffuser is preferably a surface diffuser. A surfacediffuser is easily altered in pre and post-manufacture processes toachieve a macro diffusion efficiency variation. Further, a surfacediffuser utilizes with its rough surface exposed to air, affording thelargest possible difference in index of refraction between the materialof the diffuser and the surrounding medium and, consequently, thelargest angular spread for incident light and very efficient diffusion.

[0089] In another embodiment of the invention, a bulk diffuser ispreferred. A bulk diffuser can be manufactured with a macro diffusionefficiency variation, or can be subjected to a post-manufacturingprocess to produce the variation. Further, the bulk diffuser relies onindex of refraction changes through the film, not needing an airinterface to work efficiently.

[0090] The light diffuser comprising a surface microstructure ispreferred. A surface microstructure is easily altered in design of thesurface structures and altered in a post-manufacture process to achievea macro diffusion efficiency variation. Microstructures can be tuned fordifferent diffusion efficiencies and how much they spread light.Examples of microstructures are a simple or complex lenses, prisms,pyramids, and cubes. The shape, geometry, and size of themicrostructures can be changed to accomplish the desired diffusionchange. A surface diffuser utilizes with its rough surface exposed toair, affording the largest possible difference in index of refractionbetween the material of the diffuser and the surrounding medium and,consequently, the largest angular spread for incident light and veryefficient diffusion.

[0091] There are two main ways to produce a variable diffusion film,either a pre-manufacturing or a post-manufacturing process step.

[0092] Post-manufacturing, the lenses on the complex lens diffuser,voids in the bulk voided diffuser, or surface texture on a surfacediffuser can be altered using heat and/or pressure. The process where aheat and/or pressure gradient or pattern is preferred to produce avariable diffusion film. When heat is applied to a polymeric film, thepolymer diffusion element partially or fully melts and cools to form anew structure. In the case of the complex lens surface diffuser, heatwill melt the lenses (which are made by a thermoplastic) and will reformto create new shaped lenses or a smooth polymer surface. This smoothpolymer film allows light to pass through specularly. Heat is a way toselectively turn parts of the diffuser sheet into a partially diffuse orspecular sheet and can be applied in a very precise way to createspecular dots, lines, patterns, and text. Heat applied to a voidedpolymer diffuser will melt the polymer and close the voids to the extentat which the heat is applied. The voids can be partially melted and lessdiffuse, or melted completely creating a specular region in the bulkvoided diffuser.

[0093] Pressure can also be used to modify the diffusion properties onselective areas of the diffusion film. Post-manufacturing, the lenses onthe complex lens diffuser, voids in the bulk voided diffuser, or surfacetexture on a surface diffuser can be altered using pressure. The processpressure gradient or pattern is preferred to produce a variablediffusion film. When pressure is applied to a polymeric film, thepolymer diffusion element partially or fully compresses to form a newstructure. In the case of the complex lens surface diffuser, thepressure will compress the lenses (which are made by a thermoplastic)and will reform them to create new flatter lenses (partially diffuse) ora smooth polymer surface (specular). This smooth polymer film is almostall specular. The amount of pressure needed to alter the diffusionelements depends on the materials (polymer) used and the thickness ofthe diffuser. Pressure is a way to selectively turn parts of thediffuser sheet into a specular sheet and can be applied in a veryprecise way to create specular dots, lines, patterns, and text. Pressureapplied to a voided polymer diffuser will compress the polymer and closethe voids depending on how much pressure is applied. The voids can bepartially closed and less diffuse, or closed completely creating aspecular region in the bulk voided diffuser. Post-manufacture, heat andpressure together or separately can selectively alter the diffusioncharacteristics of the diffusion films varying from diffuse to specular.

[0094] An example of a post-manufacturing process is using a thermalprint head (heat and pressure) to melt the low Tg complex lenses on acomplex lens diffuser. As the printer prints, with just a carrier sheetwith no coloration dyes or pigments, the printer head heats the polymersheet and supplies pressure to deform or completely melt the complexlens. The resolution of the areas of diffuse, semi-diffuse and speculardepends on the resolution of the print head.

[0095] Pre-manufacturing processes that can alter the diffusioncharacteristics of diffusion films selectively with respect to locationby changing the diffusion elements, such as, lenses on the complex lensdiffuser, voids in the bulk voided diffuser, or surface texture on asurface diffuser are preferred. Pre-manufacturing processes to alterdiffusion efficiencies of complex lenses are changes in the size, aspectratio, frequency and complexity of the complex lenses. This is achievedby changing the complex lens pattern on the master chill roll. The chillroll is produced from bead or particle blasting and then chroming.Varying the bead or particle blasting (size, number of particles,velocity of particles, etc) or by varying the chroming processselectively on the chill roll surface produces a master chill roll withmacro diffusion efficiency variation. This variation can be from themost diffusion all the way to no diffusion where a specular region ofthe film would be produced. (To produce a specular region in the filmthe chill roll would be flat or have no surface structure to it.) Thispre-manufacturing process can create diffusion gradients, patterns, oreven text.

[0096] Pre-manufacturing processes can alter the diffusioncharacteristics of voided diffusion films selectively with respect tolocation by changing the diffusion elements voids in the bulk voideddiffuser. Thickness of the voided layer and void attributes are twoparameters to change the diffusion efficiency in the voided diffuserversus distance. The voided layer thickness can be extruded in varyingthickness across the diffuser sheet or can be stretched more inselective areas than others. These thickness differences cause macrodiffusion efficiency variation. Void characteristics can also be alteredpre-manufacturing to develop diffusion efficiency changes. For example,the size of the void initiating bead can vary from location to locationcausing different sized voids. The concentration of void initiatingbeads can also be tailored around the diffuser sheet to create morevoids in certain areas than other areas.

[0097] In other surface diffusers, the pattern on the master roll can betailored in selective areas to create more diffuse and more specularareas. In the case of beads coated in a matrix, the beads that arecoated could vary in size or concentration. For example, while coating,larger beads could be pumped into the coating station, or a gradient ofsizes or concentrations of beads could be coated across the web creatinga diffusion efficiency gradient.

[0098] The method of applying color to a macro efficiency variation filmcomprising color transfer is preferred. The methods of applying colorcomprising ink jet printing and flexo, gravure, and screen printing arepreferred. Flexo, gravure, and screen printing and inkjet printing havea large color gamut and are quickly and easily applied to the variablediffuser film. Printing and inkjet do not apply heat or pressure so thatapplying the colorant does not change the diffusion characteristics ofthe film. This is advantaged because the diffusion element can bealtered either pre or post-manufacture and then colored selectivity withvarying colors and densities. Preferably, electrophotography appliescolor to the variable diffusion efficiency film. In another embodiment,thermal dye sublimation to apply color to the variable diffusionefficiency film is preferred. Electrophotography and thermal dyesublimation are preferred because the act of adding color to the filmcan alter the diffusion elements and the diffusion characteristics, byadding heat and pressure while printing. Adding color and changing thediffusion characteristics of the diffusion film can be accomplished inone step thereby eliminating the need for a separate diffusivityalteration step thereby saving manufacturing time and money.Furthermore, electrophotography and thermal printing have a large colorgamut and are quickly and easily applied to a variable diffuser film.

[0099] An example of creating a colored diffusion element is using athermal print head with a carrier sheet containing coloration dyes orpigments. The printer head heats the polymer sheet and supplies pressureto transfer the colored element.

[0100] A media comprising a colored macro diffusion efficiency variationthat forms graphics, text, or images is preferred. This media could be,for example: a commercial backlit display application, signage, or agreeting card. Combining variable diffusion with variable selectivecoloration creates a unique display media. For example, a greeting cardcould have green specular lettering on a neutral diffuser with red andgreen shapes surrounding the text. Currently in the art, printing colorson a diffusion film could not change the variable diffuser, whereas inthe invention, one can create areas of specular coloration in thediffuser.

[0101]FIG. 1 illustrates a cross section of a variable light diffusionfilm suitable for use in a liquid crystal display device. Coloredvariable light diffusion film 12 comprises transparent polymer base 20,onto which major lenses 22 are applied to the surface of transparentpolymer base 26. Minor lenses 24 are on the surface of the major lens22. The complex lens 30 remains intact after diffusivity alteration andcoloration. Flattened complex lens 32 has been flatted due to haet andpressure in the process of applying yellow coloration 34. Yellowcoloration 34 is on the surface of flattened complex lens 32. Thesevariations in the geometry and number of minor lenses per major lens,along with frequency of complex lenses, produce the macro diffusionefficiency variation. The invention comprises a plurality of minorlenses 24 on the surface of the major lens 22. The light diffuser of theinvention contains many diffusion surfaces from the major lens 22 andthe minor lenses 24.

[0102]FIG. 2 illustrates a liquid crystal display device with a coloredvariable light diffusion film 12. Visible light source 18 is illuminatedand light is guided into light guide 2. Lamp reflector 4 is used todirect light energy into the light guide 2, represented by an acrylicbox. Reflection tape 6, reflection tape 10 and reflection film 8 areutilized to keep light energy from exiting the light guide 2 in anunwanted direction. The colored variable light diffusion film 12 isutilized to diffuse light energy exiting the light guide in a directionperpendicular to the light diffuser. Brightness enhancement film 14 isutilized to focus the light energy into polarization film 16. Thecolored variable light diffusion film 12 is in contact with brightnessenhancement film 14.

[0103] For the light diffuser of the invention, micro-voided compositebiaxially oriented polyolefin sheets are preferred and are manufacturedby co-extrusion of the core and surface layer(s), followed by biaxialorientation, whereby voids are formed around void-initiating materialcontained in the core layer. For the biaxially oriented layer, suitableclasses of thermoplastic polymers for the biaxially oriented sheet andthe core matrix-polymer of the preferred composite sheet comprisepolyolefins. Suitable polyolefins include polypropylene, polyethylene,polymethylpentene, polystyrene, polybutylene and mixtures thereof.Polyolefin copolymers, including copolymers of propylene and ethylenesuch as hexene, butene, and octene are also useful. Polyethylene ispreferred, as it is low in cost and has desirable strength properties.Such composite sheets are disclosed in, for example, U.S. Pat. Nos.4,377,616; 4,758,462 and 4,632,869, the disclosure of which isincorporated for reference. The light diffuser film comprises a polymersheet with at least one voided polymer layer and could contain nonvoidedpolyester polymer layer(s). It should comprise a void space betweenabout 2 and 60% by volume of said voided layer of said polymer sheet.Such a void concentration is desirable to optimize the transmission andreflective properties while providing adequate diffusing power to hideback lights and filaments. The thickness of the micro void-containingoriented film of the present invention is preferably about 1 micrometerto 400 micrometer, more preferably 5 micrometer to 200 micrometer. Apolymer sheet having a percent transmission greater than 65%.

[0104] The light diffuser of the invention is preferably provided with aone or more nonvoided skin layers adjacent to the microvoided layer. Thenonvoided skin layers of the composite sheet can be made of the samepolymeric materials as listed above for the core matrix. The compositesheet can be made with skin(s) of the same polymeric material as thecore matrix, or it can be made with skin(s) of different polymericcomposition than the core matrix. For compatibility, an auxiliary layercan be used to promote adhesion of the skin layer to the core. Anysuitable polyester sheet may be utilized for the member provided that itis oriented. The orientation provides added strength to the multi-layerstructure that provides enhanced handling properties when displays areassembled. Microvoided oriented sheets are preferred because the voidsprovide opacity without the use of TiO₂. Microvoided layers areconveniently manufactured by co-extrusion of the core and thin layers,followed by biaxial orientation, whereby voids are formed aroundvoid-initiating material contained in the thin layers.

[0105] Polyester microvoided light diffusers are also preferred asoriented polyester has excellent strength, impact resistance andchemical resistance. The polyester utilized in the invention should havea glass transition temperature between about 50.degree. C. and about150.degree. C., preferably about 60-100.degree. C., should beorientable, and have an intrinsic viscosity of at least 0.50, preferably0.6 to 0.9. Suitable polyesters include those produced from aromatic,aliphatic, or cyclo-aliphatic dicarboxylic acids of 4-20 carbon atomsand aliphatic or alicyclic glycols having from 2-24 carbon atoms.Examples of suitable dicarboxylic acids include terephthalic,isophthalic, phthalic, naphthalene dicarboxylic acid, succinic,glutaric, adipic, azelaic, sebacic, fumaric, maleic, itaconic,1,4-cyclohexanedicarboxylic, sodiosulfoiso-phthalic, and mixturesthereof. Examples of suitable glycols include ethylene glycol, propyleneglycol, butanediol, pentanediol, hexanediol, 1,4-cyclohexane-dimethanol,diethylene glycol, other polyethylene glycols and mixtures thereof. Suchpolyesters are well known in the art and may be produced by well-knowntechniques, e.g., those described in U.S. Pat. Nos. 2,465,319 and2,901,466. Preferred continuous matrix polymers are those having repeatunits from terephthalic acid or naphthalene dicarboxylic acid and atleast one glycol selected from ethylene glycol, 1,4-butanediol, and1,4-cyclohexanedimethanol. Poly(ethylene terephthalate), which may bemodified by small amounts of other monomers, is especially preferred.Polypropylene is also useful. Other suitable polyesters include liquidcrystal copolyesters formed by the inclusion of a suitable amount of aco-acid component such as stilbene dicarboxylic acid. Examples of suchliquid crystal copolyesters are those disclosed in U.S. Pat. Nos.4,420,607; 4,459,402; and 4,468,510.

[0106] The co-extrusion, quenching, orienting, and heat setting ofpolyester diffuser sheets may be effected by any process which is knownin the art for producing oriented sheet, such as by a flat sheet processor a bubble or tubular process. The flat sheet process involvesextruding the blend through a slit die and rapidly quenching theextruded web upon a chilled casting drum so that the core matrix polymercomponent of the sheet and the skin components(s) are quenched belowtheir glass solidification temperature. The quenched sheet is thenbiaxially oriented by stretching in mutually perpendicular directions ata temperature above the glass transition temperature, below the meltingtemperature of the matrix polymers. The sheet may be stretched in onedirection and then in a second direction or may be simultaneouslystretched in both directions. After the sheet has been stretched, it isheat set by heating to a temperature sufficient to crystallize or annealthe polymers while restraining to some degree the sheet againstretraction in both directions of stretching.

[0107] Additional layers preferably are added to the micro-voidedpolyester diffusion sheet that may achieve a different effect. Suchlayers might contain tints, antistatic materials, or differentvoid-making materials to produce sheets of unique properties. Biaxiallyoriented sheets could be formed with surface layers that would providean improved adhesion. The biaxially oriented extrusion could be carriedout with as many as 10 layers if desired to achieve some particulardesired property.

[0108] Addenda are preferably added to a polyester skin layer to changethe color of the imaging element. Colored pigments that can resistextrusion temperatures greater than 320 degrees Celsius are preferred,as temperatures greater than 320 degrees Celsius are necessary forco-extrusion of the skin layer.

[0109] The polyester light diffuser may be coated or treated after theco-extrusion and orienting process or between casting and fullorientation with any number of coatings which may be used to improve theproperties of the sheets including printability, to provide a vaporbarrier, to make them heat sealable, or to improve adhesion. Examples ofthis would be acrylic coatings for printability, coating polyvinylidenechloride for heat seal properties. Further examples include flame,plasma or corona discharge treatment to improve printability oradhesion. By having at least one nonvoided skin on the micro-voidedcore, the tensile strength of the sheet is increased and makes it moremanufacturable. It allows the sheets to be made at wider widths andhigher draw ratios than when sheets are made with all layers voided. Thenon-voided layer(s) can be peeled off after. manufacture of the film.Co-extruding the layers further simplifies the manufacturing process.

[0110] The light diffuser of the present invention may be used incombination with one or more layers selected from an opticalcompensation film, a polarizing film and a substrate constitution aliquid crystal layer. The oriented film of the present invention ispreferably used by a combination of oriented film/polarizingfilm/optical compensation film in the order. In the case of using theabove films in combination in a liquid crystal display device, the filmsare preferably bonded with each other e.g. through a tacky adhesive forminimizing the reflection loss, etc. The tacky adhesive is preferablythose having a refractive index close to that of the oriented film tosuppress the interfacial reflection loss of light.

[0111] The light diffusion of the present invention may be used incombination with a film or sheet made of a transparent polymer. Examplesof such polymer are polyesters such as polycarbonate, polyethyleneterephthalate, polybutylene terephthalate and polyethylene naphthalate,acrylic polymers such as polymethyl methacrylate, and polyethylene,polypropylene, polystyrene, polyvinyl chloride, polyether sulfone,polysulfone, polyarylate and triacetyl cellulose. The light diffuser maybe mounted to a glass sheet for support.

[0112] The light diffuser of the present invention may be incorporatedwith e.g. an additive or a lubricant such as silica for improving thedrawability and the surface-slipperiness of the film within a range notto deteriorate the optical characteristics to vary the light-scatteringproperty with an incident angle. Examples of such additive are organicsolvents such as xylene, alcohols or ketones, fine particles of anacrylic resin, silicone resin or Δ metal oxide or a filler.

[0113] The light diffuser of the present invention usually have opticalanisotropy. A biaxially drawn film of a thermoplastic polymer isgenerally an optically anisotropic material exhibiting opticalanisotropy having an optic axis in the drawing direction. The opticalanisotropy is expressed by the product of the film thickness d and thebirefringence Δn which is a difference between the refractive index inthe slow optic axis direction and the refractive index in the fast opticaxis direction in the plane of the film, i.e. Δn*d (retardation). Theorientation direction coincides with the drawing axis in the film of thepresent invention. The drawing axis is the direction of the slow opticaxis in the case of a thermoplastic polymer having a positive intrinsicbirefringence and is the direction of the fast optic axis for athermoplastic polymer having a negative intrinsic birefringence. Thereis no definite requirement for the necessary level of the value of Δn.*dsince the level depends upon the application of the film, however, it ispreferably 50 nm or more.

[0114] The microvoid-containing oriented film of the present inventionhas a function to diffuse the light. A periodically varying refractiveindex distribution formed by these numerous microvoids and micro-lensformed by the micro voided forms a structure like a diffraction gratingto contribute to the optical property to scatter the light. The voidedthermoplastic diffuser sheet provides excellent scattering of lightwhile having a high % light transmission. “Void” is used herein to meandevoid of added solid and liquid matter, although it is likely the“voids” contain gas. The void-initiating particles which remain in thefinished packaging sheet core should be from 0.1 to 10 micrometers indiameter, preferably round in shape, to produce voids of the desiredshape and size. Voids resulting from the use of initiating particles ofthis size are termed “microvoids” herein. The voids exhibit a dimensionof 10 micrometers or less in the unoriented thickness or Z direction ofthe layer. The size of the void is also dependent on the degree oforientation in the machine and transverse directions. Ideally, the voidwould assume a shape which is defined by two opposed and edge contactingconcave disks. In other words, the voids tend to have a substantiallycircular cross section in the plane perpendicular to the direction ofthe light energy (also termed the vertical direction herein). The voidsare oriented so that the two major dimensions (major axis and minoraxis) are aligned with the machine and transverse directions of thesheet. The Z-direction axis is a minor dimension and is roughly the sizeof the cross diameter of the voiding particle. The voids generally tendto be closed cells, and thus there is virtually no path open from oneside of the voided-core to the other side through which gas or liquidcan traverse.

[0115] Microvoids formed from organic spheres are preferred because theyare low in light scattering, have been shown to form substantiallycircular voids and are easily dispersed in polyester. Further, the sizeand the shape of the voided diffuser layer can be changed by properselection of organic sphere size and amount. Microvoids that aresubstantially free of scattering inorganic particles is also preferred.Prior art voided polymer layers that use inorganic particles such asclay, TiO₂ and silica have been shown to unacceptably scatter visiblelight energy. Scattering light energy from the back light source reducesthe efficiency of the display unit by scattering light energy away fromthe LC and back toward the light source. It has been shown thatinorganic microvoiding particles can cause as much as 8% loss intransmitted light energy.

[0116] Substantially circular voids, or voids whose major axis to minoraxis is between 2.0 and 0.5 are preferred as substantially circularvoids have been shown to provide efficient diffusion of light energy andreduce uneven diffusion of light energy. A major axis diameter to minoraxis diameter ratio of less than 2.0 is preferred. A ratio less than 2.0has been shown to provide excellent diffusion of LC light sources.Further, a ratio greater than 3.0 yields voids that are spherical andspherical voids have been shown to provide uneven dispersion of light. Aratio between 1.0 and 1.6 is most preferred as light diffusion and lighttransmission is optimized.

[0117] A microvoid is a void in the polymer layer of the diffuser thathas a volume less than 100 micrometers. Microvoids larger than 100micrometers are capable of diffusing visible light, however, because thevoid size is large, uneven diffusion of the light occurs resulting inuneven lighting of display devices. A thermoplastic microvoid volumebetween 8 and 42 cubic micrometers is preferred. A microvoided volumeless than 6 cubic micrometers is difficult to obtain as the voidingagent required for 6 cubic micrometers is to small to void with typical3×3 orientation of polyester. A microvoid volume greater than 50 cubicmicrometers, while providing diffusion, creates a thick diffusion layerrequiring extra material and cost. The most preferred void volume forthe thermoplastic diffuser is between 10 and 20 cubic micrometers.Between 10 and 20 cubic micrometers has been shown to provide excellentdiffusion and transmission properties.

[0118] The organic void-initiating material may be selected from avariety of materials, and should be present in an amount of about 5 to50% by weight based on the weight of the core matrix polymer.Preferably, the void-initiating material comprises a polymeric material.When a polymeric material is used, it may be a polymer that can bemelt-mixed with the polymer from which the core matrix is made and beable to form dispersed spherical particles as the suspension is cooleddown. Examples of this would include nylon dispersed in polypropylene,polybutylene terephthalate in polypropylene, or polypropylene dispersedin polyethylene terephthalate. If the polymer is pre-shaped and blendedinto the matrix polymer, the important characteristic is the size andshape of the particles. Spheres are preferred and they can be hollow orsolid. These spheres may be made from cross-linked polymers whichinclude members selected from the group consisting of an alkenylaromatic compound having the general formula Ar—C(R)═CH₂, wherein Arrepresents an aromatic hydrocarbon radical, or an aromatichalohydrocarbon radical of the benzene series and R is hydrogen or themethyl radical; acrylate-type monomers including monomers of the formulaCH₂═C(R′)C(O)(OR) wherein R is selected from the group consisting ofhydrogen and an alkyl radical containing from about 1 to 12 carbon atomsand R′ is selected from the group consisting of hydrogen and methyl;copolymers of vinyl chloride and vinylidene chloride, acrylonitrile andvinyl chloride, vinyl bromide, vinyl esters having formula CH₂═CH(O)COR,wherein R is an alkyl radical containing from 2 to 18 carbon atoms;acrylic acid, methacrylic acid, itaconic acid, citraconic acid, maleicacid, fumaric acid, oleic acid, vinylbenzoic acid; the syntheticpolyester resins which are prepared by reacting terephthalic acid anddialkyl terephthalics or ester-forming derivatives thereof, with aglycol of the series HO(CH₂)_(n)OH wherein n is a whole number withinthe range of 2-10 and having reactive olefinic linkages within thepolymer molecule, the above described polyesters which includecopolymerized therein up to 20 percent by weight of a second acid orester thereof having reactive olefinic unsaturation and mixturesthereof, and a cross-linking agent selected from the group consisting ofdivinylbenzene, diethylene glycol dimethacrylate, diallyl fumarate,diallyl phthalate, and mixtures thereof.

[0119] Preferred crosslinked polymer beads have a mean particle sizeless than 2.0 micrometers, more preferably between 0.3 and 1.7micrometers. Crosslinked polymer beads smaller than 0.3 micrometers areprohibitively expensive. Crosslinked polymer beads larger than 1.7micrometers make voids that large and do not scatter light efficiently.

[0120] Examples of typical monomers for making the cross-linked polymerinclude styrene, butyl acrylate, acrylamide, acrylonitrile, methylmethacrylate, ethylene glycol dimethacrylate, vinyl pyridine, vinylacetate, methyl acrylate, vinylbenzyl chloride, vinylidene chloride,acrylic acid, divinylbenzene, arylamidomethyl-propane sulfonic acid,vinyl toluene, etc. Preferably, the cross-linked polymer is polystyreneor poly(methyl methacrylate). Most preferably, it is polystyrene and thecross-linking agent is divinylbenzene.

[0121] Processes well known in the art yield non-uniformly sizedparticles, characterized by broad particle size distributions. Theresulting beads can be classified by screening to produce beads spanningthe range of the original distribution of sizes. Other processes such assuspension polymerization and limited coalescence directly yield veryuniformly sized particles. U.S. Pat. No. 6,074,788, the disclosure ofwhich is incorporated for reference. It is preferred to use the “limitedcoalescence” technique for producing the coated, cross-linked polymermicrobeads. This process is described in detail in U.S. Pat. No.3,615,972. Preparation of the coated microbeads for use in the presentinvention does not utilize a blowing agent as described in this patent,however. Suitable slip agents or lubricants include colloidal silica,colloidal alumina, and metal oxides such as tin oxide and aluminumoxide. The preferred slip agents are colloidal silica and alumina, mostpreferably, silica. The cross-linked polymer having a coating of slipagent may be prepared by procedures well known in the art. For example,conventional suspension polymerization processes wherein the slip agentis added to the suspension is preferred. As the slip agent, colloidalsilica is preferred.

[0122] The microbeads of cross-linked polymer range in size from 0.1-50μm, and are present in an amount of 5-50% by weight based on the weightof the polyester. Microbeads of polystyrene should have a Tg of at least20° C. higher than the Tg of the continuous matrix polymer and are hardcompared to the continuous matrix polymer.

[0123] Elasticity and resiliency of the microbeads generally result inincreased voiding, and it is preferred to have the Tg of the microbeadsas high above that of the matrix polymer as possible to avoiddeformation during orientation. It is not believed that there is apractical advantage to cross-linking above the point of resiliency andelasticity of the microbeads.

[0124] The microbeads of cross-linked polymer are at least partiallybordered by voids. The void space in the supports should occupy 2-60%,preferably 30-50%, by volume of the film support. Depending on themanner in which the supports are made, the voids may completely encirclethe microbeads, e.g., a void may be in the shape of a doughnut (orflattened doughnut) encircling a micro-bead, or the voids may onlypartially border the microbeads, e.g., a pair of voids may border amicrobead on opposite sides.

[0125] During stretching the voids assume characteristic shapes from thebalanced biaxial orientation of films to the uniaxial orientation ofmicrovoided films. Balanced microvoids are largely circular in the planeof orientation. The size of the microvoids and the ultimate physicalproperties depend upon the degree and balance of the orientation,temperature and rate of stretching, crystallization kinetics, the sizedistribution of the microbeads, and the like. The film supportsaccording to this invention are prepared by: (a) forming a mixture ofmolten continuous matrix polymer and cross-linked polymer wherein thecross-linked polymer is a multiplicity of microbeads uniformly dispersedthroughout the matrix polymer, the matrix polymer being as describedhereinbefore, the cross-linked polymer microbeads being as describedhereinbefore, (b) forming a film support from the mixture by extrusionor casting, (c) orienting the article by stretching to form microbeadsof cross-linked polymer uniformly distributed throughout the article andvoids at least partially bordering the microbeads on sides thereof inthe direction, or directions of orientation.

[0126] Methods of bilaterally orienting sheet or film material are wellknown in the art. Basically, such methods comprise stretching the sheetor film at least in the machine or longitudinal direction after it iscast or extruded an amount of about 1.5-10 times its original dimension.Such sheet or film may also be stretched in the transverse orcross-machine direction by apparatus and methods well known in the art,in amounts of generally 1.5-10 (usually 3-4 for polyesters and 6-10 forpolypropylene) times the original dimension. Such apparatus and methodsare well known in the art and are described in such U.S. Pat. No.3,903,234.

[0127] The voids, or void spaces, referred to herein surrounding themicrobeads are formed as the continuous matrix polymer is stretched at atemperature above the Tg of the matrix polymer. The microbeads ofcross-linked polymer are relatively hard compared to the continuousmatrix polymer. Also, due to the incompatibility and immiscibilitybetween the microbead and the matrix polymer, the continuous matrixpolymer slides over the microbeads as it is stretched, causing voids tobe formed at the sides in the direction or directions of stretch, whichvoids elongate as the matrix polymer continues to be stretched. Thus,the final size and shape of the voids depends on the direction(s) andamount of stretching. If stretching is only in one direction, microvoidswill form at the sides of the microbeads in the direction of stretching.If stretching is in two directions (bidirectional stretching), in effectsuch stretching has vector components extending radially from any givenposition to result in a doughnut-shaped void surrounding each microbead.

[0128] The preferred preform stretching operation simultaneously opensthe microvoids and orients the matrix material. The final productproperties depend on and can be controlled by stretchingtime-temperature relationships and on the type and degree of stretch.For maximum opacity and texture, the stretching is done just above theglass transition temperature of the matrix polymer. When stretching isdone in the neighborhood of the higher glass transition temperature,both phases may stretch together and opacity decreases. In the formercase, the materials are pulled apart, a mechanical anticompatibilizationprocess.

[0129] In general, void formation occurs independent of, and does notrequire, crystalline orientation of the matrix polymer. Opaque,microvoided films have been made in accordance with the methods of thisinvention using completely amorphous, noncrystallizing copolyesters asthe matrix phase. Crystallizable/orientable (strain hardening) matrixmaterials are preferred for some properties like tensile strength andgas transmission barrier. On the other hand, amorphous matrix materialshave special utility in other areas like tear resistance and beatsealability. The specific matrix composition can be tailored to meetmany product needs. The complete range from crystalline to amorphousmatrix polymer is part of the invention.

[0130] The complex lenses of the invention preferably comprise polymers.Polymers are preferred as they are generally lower in cost compared toprior art glass lenses, have excellent optical properties and can beefficiently formed into lenses utilizing known processes such as meltextrusion, vacuum forming and injection molding. Preferred polymers forthe formation of the complex lenses include polyolefins, polyesters,polyamides, polycarbonates, cellulosic esters, polystyrene, polyvinylresins, polysulfonamides, polyethers, polyimides, polyvinylidenefluoride, polyurethanes, polyphenylenesulfides, polytetrafluoroethylene,polyacetals, polysulfonates, polyester ionomers, and polyolefinionomers. Copolymers and/or mixtures of these polymers to improvemechanical or optical properties can be used. Preferred polyamides forthe transparent complex lenses include nylon 6, nylon 66, and mixturesthereof. Copolymers of polyamides are also suitable continuous phasepolymers. An example of a useful polycarbonate is bisphenol-Apolycarbonate. Cellulosic esters suitable for use as the continuousphase polymer of the complex lenses include cellulose nitrate, cellulosetriacetate, cellulose diacetate, cellulose acetate propionate, celluloseacetate butyrate, and mixtures or copolymers thereof. Preferredpolyvinyl resins include polyvinyl chloride, poly(vinyl acetal), andmixtures thereof. Copolymers of vinyl resins can also be utilized.Preferred polyesters for the complex lens of the invention include thoseproduced from aromatic, aliphatic or cycloaliphatic dicarboxylic acidsof 4-20 carbon atoms and aliphatic or alicyclic glycols having from 2-24carbon atoms. Examples of suitable dicarboxylic acids includeterephthalic, isophthalic, phthalic, naphthalene dicarboxylic acid,succinic, glutaric, adipic, azelaic, sebacic, fumaric, maleic, itaconic,1,4-cyclohexanedicarboxylic, sodiosulfoisophthalic and mixtures thereof.Examples of suitable glycols include ethylene glycol, propylene glycol,butanediol, pentanediol, hexanediol, 1,4-cyclohexanedimethanol,diethylene glycol, other polyethylene glycols and mixtures thereof.

[0131] The diffuser sheets may be coated or treated before or afterthermoplastic lenslet casting with any number of coatings which may beused to improve the properties of the sheets including printability, toprovide a vapor barrier, to make them heat sealable, or to improveadhesion. Examples of this would be acrylic coatings for printability,coating polyvinylidene chloride for heat seal properties. Furtherexamples include flame, plasma or corona discharge treatment to improveprintability or adhesion.

[0132] The light diffuser of the invention may also be used inconjunction with another light diffuser, for example a bulk diffuser, alenticular layer, a beaded layer, a surface diffuser, a holographicdiffuser, a micro-structured diffuser, another lens array, or variouscombinations thereof. The lenslet diffuser film disperses, or diffuses,the light, thus destroying any diffraction pattern that may arise fromthe addition of an ordered periodic lens array. The lenslet diffuserfilm may be positioned before or after any diffuser or lens array.

[0133] The invention can also include, in another aspect, one or moreoptical coatings to improve optical transmission through one or morelenslet channels. It is often desirable to coat a diffuser with a layerof an anti-reflective (AR) coating in order to raise the efficiency ofthe diffuser.

[0134] In the manufacturing process for the complex lens light diffuserfilms of the present invention, preferred lens polymers are meltextruded from a slit die. In general, a T die or a coat hanger die arepreferably used. The process involves extruding the polymer or polymerblend through a slit die and rapidly quenching the extruded web upon achilled casting drum with the preferred lens geometry so that the lenspolymer component of the transparent sheet are quenched below theirglass solidification temperature and retain the shape of the diffusionlens.

[0135] A method of fabricating a diffusion film assembly was developed.The preferred approach comprises the steps of providing a positivemaster chill roll having a plurality of complex lenses. The diffusionfilm is replicated from the master chill roller by casting a moltenpolymeric material to the face of the chill roll and transferring thepolymeric material with lenslet structures onto a base.

[0136] A chill roller is manufactured by a process including the stepsof electroplating a layer of cooper onto the surface of a roller, andthen abrasively blasting the surface of the copper layer with beads,such as glass or silicon dioxide, to create a surface texture withhemispherical features. The resulting blasted surface is bright nickelelectroplated or chromed to a depth that results in a surface texturewith the features either concave into the roll or convex out of theroll. Because of the release characteristics of the chill roll surface,the resin will not adhere to the surface of the roller.

[0137] The bead blasting operation is carried out using an automateddirect pressure system in which the nozzle feed rate, nozzle distancefrom the roller surface, the roller rotation rate during the blastingoperation and the velocity of the particles are accurately controlled tocreate the desired lenslet structure.

[0138] The number of features in the chill roll per area is determinedby the bead size and the pattern depth. Larger bead diameters and deeperpatterns result in fewer numbers of features in a given area. Thereforethe number of features is inherently determined by the bead size and thepattern depth.

[0139] The complex lenses of the invention may also be manufactured byvacuum forming around a pattern, injection molding the lenses andembossing lenses in a polymer web. While these manufacturing techniquesdo yield acceptable lenses capable of efficiently diffusing light, meltcast coating polymer onto a patterned roll and subsequent transfer ontoa transparent polymer web allows for the lenses of the invention to beformed into rolls thereby lowering the manufacturing cost for thediffusion lenses. Further, cast coating polymer has been shown to moreefficiently replicate the desired complex lens geometry compared toembossing and vacuum forming.

[0140] The invention may be used in conjunction with any liquid crystaldisplay devices, typical arrangements of which are described in thefollowing. Liquid crystals (LC) are widely used for electronic displays.In these display systems, an LC layer is situated between a polarizerlayer and an analyzer layer and has a director exhibiting an azimuthaltwist through the layer with respect to the normal axis. The analyzer isoriented such that its absorbing axis is perpendicular to that of thepolarizer. Incident light polarized by the polarizer passes through aliquid crystal cell is affected by the molecular orientation in theliquid crystal, which can be altered by the application of a voltageacross the cell. By employing this principle, the transmission of lightfrom an external source, including ambient light, can be controlled. Theenergy required to achieve this control is generally much less than thatrequired for the luminescent materials used in other display types suchas cathode ray tubes. Accordingly, LC technology is used for a number ofapplications, including but not limited to digital watches, calculators,portable computers, electronic games for which light weight, low powerconsumption and long operating life are important features.

[0141] Active-matrix liquid crystal displays (LCDs) use thin filmtransistors (TFTs) as a switching device for driving each liquid crystalpixel. These LCDs can display higher-definition images without crosstalk because the individual liquid crystal pixels can be selectivelydriven. Optical mode interference (OMI) displays are liquid crystaldisplays, which are “normally white,” that is, light is transmittedthrough the display layers in the off state. Operational mode of LCDusing the twisted nematic liquid crystal is roughly divided into abirefringence mode and an optical rotatory mode. “Film-compensatedsuper-twisted nematic” (FSTN) LCDs are normally black, that is, lighttransmission is inhibited in the off state when no voltage is applied.OMI displays reportedly have faster response times and a broaderoperational temperature range.

[0142] Ordinary light from an incandescent bulb or from the sun israndomly polarized, that is, it includes waves that are oriented in allpossible directions. A polarizer is a dichroic material that functionsto convert a randomly polarized (“unpolarized”) beam of light into apolarized one by selective removal of one of the two perpendicularplane-polarized components from the incident light beam. Linearpolarizers are a key component of liquid-crystal display (LCD) devices.

[0143] There are several types of high dichroic ratio polarizerspossessing sufficient optical performance for use in LCD devices. Thesepolarizers are made of thin sheets of materials which transmit onepolarization component and absorb the other mutually orthogonalcomponent (this effect is known as dichroism). The most commonly usedplastic sheet polarizers are composed of a thin, uniaxially-stretchedpolyvinyl alcohol (PVA) film which aligns the PVA polymer chains in amore-or-less parallel fashion. The aligned PVA is then doped with iodinemolecules or a combination of colored dichroic dyes (see, for example,EP 0 182 632 A2, Sumitomo Chemical Company, Limited) which adsorb to andbecome uniaxially oriented by the PVA to produce a highly anisotropicmatrix with a neutral gray coloration. To mechanically support thefragile PVA film it is then laminated on both sides with stiff layers oftriacetyl cellulose (TAC), or similar support.

[0144] Contrast, color reproduction, and stable gray scale intensitiesare important quality attributes for electronic displays, which employliquid crystal technology. The primary factor limiting the contrast of aliquid crystal display is the propensity for light to “leak” throughliquid crystal elements or cell, which are in the dark or “black” pixelstate. Furthermore, the leakage and hence contrast of a liquid crystaldisplay are also dependent on the angle from which the display screen isviewed. Typically the optimum contrast is observed only within a narrowviewing angle centered about the normal incidence to the display andfalls off rapidly as the viewing angle is increased. In color displays,the leakage problem not only degrades the contrast but also causes coloror hue shifts with an associated degradation of color reproduction. Inaddition to black-state light leakage, the narrow viewing angle problemin typical twisted nematic liquid crystal displays is exacerbated by ashift in the brightness-voltage curve as a function of viewing anglebecause of the optical anisotropy of the liquid crystal material.

[0145] The colored variable diffusion film of the present invention caneven out the luminance when the film is used as a light-scattering filmin a backlight system. Back-lit LCD display screens, such as areutilized in portable computers, may have a relatively localized lightsource (ex. fluorescent light) or an array of relatively localized lightsources disposed relatively close to the LCD screen, so that individual“hot spots” corresponding to the light sources may be detectable. Thediffuser film serves to even out the illumination across the display.The liquid crystal display device includes display devices having acombination of a driving method selected from e.g. active matrix drivingand simple matrix drive and a liquid crystal mode selected from e.g.twist nematic, supertwist nematic, ferroelectric liquid crystal andantiferroelectric liquid crystal mode, however, the invention is notrestricted by the above combinations. In a liquid crystal displaydevice, the oriented film of the present invention is necessary to bepositioned in front of the backlight. The diffuser film of the presentinvention can even the lightness of a liquid crystal display deviceacross the display because the film can vary to compensate for thebrightness near the light source and less light intensity away from thelight source. The variable colored light diffusers also have excellentlight-scattering properties to expand the light to give excellentvisibility in all directions. Although the above effect can be achievedeven by the single use of such variable diffuser film, plural number offilms may be used in combination. The variable diffuser film may beplaced in front an LCD to disburse light from the display further andmake it much more homogenous across the display.

[0146] The variable diffuser of the present invention can replace thedot printing on the wave guide in an LCD and at the same time correctthe light source to create a neutral illuminate for the LCD. The waveguide is typically a thick (approx half a centimeter) piece of acrylicdesigned to guide the light from the light sources out at a normal tothe display and to even the light from the back lights across thedisplay. The evening of brightness is produced by a dot pattern printedon the back side (the side facing the reflector) of the wave guide. Thedot pattern varies in size across the display to try to direct morelight out of the wave guide in the away from the light sources and lesslight out of the display near the light sources. This printing is a verycostly and time consuming because each wave guide is screen printedindividually, not like the roll to roll process of the currentinvention. Having a variable diffuser with a diffusion gradient (morediffusion near the light source and less away from it) on top of thewave guide eliminates the need for the screen printed dots thuseliminating a processing step and saving manufacturing time and money.It has been shown that selective coloration of the variable diffusercreates an even color tone across the display. For example, a displaymight have a red tint to it and the desire is to have a neutral display.The diffuser for the light source would nee to have a cyan component toit, higher in density close to the light source and lower in densityaway from the light to create an even color across the display. Usingcolored variable diffusers displays can be fabricated with evenillumination and color across the display.

[0147] The colored variable diffuser can display text, shapes, andimages in varying amounts of diffusion or specular areas and differentcolors surrounded by diffuse regions. These colored variable diffuserscan be used in displays and as overheads. As overheads the coloredvariable diffuser has added utility. In an unexpected result, when thecolored variable diffuser was placed on an overhead projector, thediffuse areas were dark, and the specular areas were bright. Thisoccurred because when the light from the light source in the overheadprojector hit the diffuse areas of the diffuser sheet, the light wasdiffused and the focusing lens did not collect the light and the imageprojected was dark. The specular areas transmitted specular lightproducing bright areas on the display. Colored variable diffusionsheets, with there ability to produce colored text, shapes, and imageswith diffuse and specular areas, can be used as project materials toimprove the contrast in the projected sheet allowing the display to bemore easily read in a bright room and producing for an unusual displayeffect.

[0148] The present invention has a significant use as a light sourcedestructuring device. In many applications, it is desirable to eliminatefrom the output of the light source itself the structure of the filamentwhich can be problematic in certain applications because lightdistributed across the sample will vary and this is undesirable. Also,variances in the orientation of a light source filament or arc after alight source is replaced can generate erroneous and misleading readings.A colored variable diffuser film of the present invention placed betweenthe light source and the detector can eliminate from the output of thelight source any trace of the filament structure and therefore causes ahomogenized output which is identical from light source to light source.

[0149] The colored variable diffuser films may be used to controllighting for stages by providing pleasing homogenized colored light thatis directed where desired. In stage and television productions, a widevariety of stage lights must be used to achieve all the differenteffects necessary for proper lighting. This requires that many differentlamps be used which is inconvenient and expensive. The films of thepresent invention placed over a lamp can give almost unlimitedflexibility dispersing light and coloring light where it is needed. As aconsequence, almost any object, moving or not, and of any shape, can becorrectly illuminated.

[0150] The colored variable diffuser can be transformed into areflection film or a transflector film by applying a reflection layercomposed of a metallic film, etc., to the colored variable diffuser filmof the present invention can be used e.g. as a retroreflective memberfor a traffic sign. It can be used in a state applied to a car, abicycle, person, etc. When the colored variable light diffuser is placedon a metallic film, it can cause the amount of reflection and diffusionreflection to vary across the film from diffuse to almost specular. Thiscan create a reflection sign with sections diffuse and sections (such astext) as a mirror surface and have colored reflections. The surface ofthe colored variable diffuser can also be partially metallized as tocreate a colored variable diffusion transflector, an optical film in aLCD so that the LCD can be used in both reflection and transmissionmode.

[0151] The colored variable diffuser films of the present invention mayalso be used in the area of law enforcement and security systems tohomogenize the output from laser diodes (LDs) or light emitting diodes(LEDs) over the entire secured area to provide higher contrasts toinfrared (IR) detectors. The films of the present invention may also beused to remove structure from devices using LED or LD sources such as inbank note readers or skin treatment devices. This leads to greateraccuracy.

[0152] The light diffuser films of the present invention can also beused to homogeneously illuminate a sample under a microscope bydestructuring the filament or arc of the source, yielding ahomogeneously illuminated field of view. The light diffusion film canhave colored variable diffusion, with a higher level of diffusion infront of the light source, and less diffusion in the areas around thelight source. The light diffuser films may also be used to homogenizethe various modes that propagate through a fiber, for example, the lightoutput from a helical-mode fiber and color the light at the same time.

[0153] The colored variable diffuser films of the present invention alsohave significant architectural uses such as providing appropriate lightfor work and living spaces. In typical commercial applications,inexpensive transparent polymeric diffuser films are used to helpdiffuse light over the room. A colored variable diffuser of the presentinvention replaces one of these conventional uniform diffusers providesa more uniform light output so that light is diffused to all anglesacross the room evenly and with no hot spots and with a pleasingcoloration.

[0154] The colored variable diffuser films of the present invention mayalso be used to diffuse light illuminating artwork. The colored variablediffuser provides a suitable appropriately sized and directed aperturefor depicting the artwork in a most desirable fashion and in the correctlighting color. For example, adding a colored variable diffuser cantransform fluorescent colored light into sunlight colored light therebyilluminating the artwork correctly.

[0155] Further, the colored variable diffuser film of the presentinvention can be used widely as a part for an optical equipment such asa displaying device. For example, it can be used as a light-reflectionplate laminated with a reflection film such as a metal film in areflective liquid crystal display device or a front scattering filmdirecting the film to the front-side (observer's side) in the case ofplacing the metallic film to the back side of the device (opposite tothe observer), in addition to the aforementioned light-scattering plateof a backlight system of a liquid crystal display device. The coloredvariable diffuser film of the present invention can be used as anelectrode by laminating a transparent conductive layer composed ofindium oxide represented by ITO film. If the material is to be used toform a reflective screen, e.g. front projection screen, alight-reflective layer is applied to the diffuser.

[0156] Another application for the variable diffuser film is a rearprojection screen, where it is generally desired to project the imagefrom a light source onto a screen over a large area. The viewing anglefor a television is typically smaller in the vertical direction than inthe horizontal direction so variable diffusion across the display cancontrol the viewing angle and brightness across the display. It would bedesirable to have the screen have a color tint for increased contrast.

[0157] Embodiments of the invention may provide not only improvedselective coloration light diffusion and transmission but also adiffusion film of reduced thickness, and that has reduced lightscattering tendencies.

[0158] The entire contents of the patents and other publicationsreferred to in this specification are incorporated herein by reference.

EXAMPLE

[0159] In this example, the colored variable light diffusion efficiencyfilm of the invention was created by extrusion casting an extrusiongrade polyolefin polymer against a pattered chill roll containing avarying complex lens geometry. The patterned polyolefin polymer, in theform the complex lens was then transferred to a polyester web materialthereby forming a light diffuser with complex surface lenses. Thisexample will show that varying size, geometry, and complexity complexsurface lenses formed on a transparent polymer web material andselective coloration will produce colored variable diffusion across adiffusion film providing exceptional colored variable light diffusion.Further, it will be obvious that the light diffuser will be low in costand have mechanical properties that allow for insertion into LC devices.

[0160] A patterned chill roll (complex lens geometry) was manufacturedby a process including the steps of electroplating a layer of cooperonto the surface of a roller, and then abrasively blasting the surfaceof the copper layer with glass beads to create a surface texture withhemispherical features. The resulting blasted surface was bright nickelelectroplated to a depth that results in a surface texture with thefeatures either concave into the roll or convex out of the roll. Thebead blasting operation was carried out using an automated directpressure system in which the nozzle feed rate, nozzle distance from theroller surface, the roller rotation rate during the blasting operationand the velocity of the particles are accurately controlled to createthe desired complex lens structure. The number of features in the chillroll per area is determined by the bead size and the pattern depth.Larger bead diameters and deeper patterns result in fewer numbers offeatures in a given area.

[0161] The complex lens patterned roll was manufactured by starting witha steel roll blank and grit blasted with size 14 grit at a pressure of447 MPa. The roll was then chrome platted. The resulting complex lenseson the surface of the roll were convex. The single lens patterned roll(control) was manufactured by starling with a copper roll blank and gritblasted with size 14 spherical grit at a pressure of 310 MPa. Theresulting single lenses on the surface of the roll were concave.

[0162] The patterned chill roll was utilized to create light diffusionsheets by extrusion coating a polyolefin polymer from a coat hanger slotdie comprising substantially 96.5% LDPE (Eastman Chemical grade D4002P),3% Zinc Oxide and 0.5% of calcium stearate onto a 100 micrometertransparent oriented web polyester web with a % light transmission of97.2%. The polyolefin cast coating coverage was 25.88 g/m².

[0163] The invention materials containing complex lenses had randomlydistributed lenses comprising a major lens with an average diameter of27.1 micrometers and minor lenses on the surface of the major lenseswith an average diameter of 6.7 micrometers. The average minor to majorlens ratio was 17.2 to 1. The structure of the cast coated diffusionsheets is as follows,

[0164] Formed polyolefin lenses

[0165] Transparent polyester base

[0166] The diffusion film was them post-manufacture colored and thediffusivity was changed selectively. The film was printed using thermaldye sublimation. The thermal print head applied heat and pressure tomelt the lenses and apply the yellow colorant from the thermal colordonor. The heat and pressure melted the lenses causing an almostcompletely specular transmission area in the film and at the same time,colored the specular area yellow. The printed feature was a 100% yellowmostly specular specular square 2 cm in length and width, though thefeature could have been any color and any size, shape, or amount ofdiffusion.

[0167] The variable diffusion film containing complex polymer lensesfrom above were measured for % light transmission and % diffuse lighttransmission, diffuse light transmission efficiency, a*, and b*. a* is ameasure of the redness or greenness and is expressed as single number,which is positive if the color is red and negative if the color isgreen. Similarly, yellowness or blueness is expressed by b*, which ispositive for yellow and negative for blue. The larger the absolute valueis for the a* and b*, the more colored the film is. The a* and b* valuesof the films were measured using a CIElab calorimeter with an 1964observer and a D65 illuminate.

[0168] The colored variable diffusion film was measured with the HitachiU4001 UV/Vis/NIR spectrophotometer equipped with an integrating sphere.The total transmittance spectra were measured by placing the samples atthe beam port with the front surface with complex lenses towards theintegrating sphere. A calibrated 99% diffusely reflecting standard(NIST-traceable) was placed at the normal sample port. The diffusetransmittance spectra were measured in like manner, but with the 99%tile removed. All spectra were acquired between 350 and 800 nm. As thediffuse reflectance results are quoted with respect to the 99% tile, thevalues are not absolute, but would need to be corrected by thecalibration report of the 99% tile.

[0169] Percentage total transmitted light refers to percent of lightthat is transmitted though the sample at all angles. Diffusetransmittance is defined as the percent of light passing though thesample excluding a 2.5 degree angle from the incident light angle. Thediffuse light transmission is the percent of light that is passedthrough the sample by diffuse transmittance. The term “diffusionefficiency” means the ratio of % diffuse transmitted light at 500 nm to% total transmitted light at 500 nm multiplied by a factor of 100, asknown as haze in the art. Diffuse reflectance is defined as the percentof light reflected by the sample. The percentages quoted in the exampleswere measured at 500 nm. These values may not add up to 100% due toabsorbencies of the sample or slight variations in the sample measured.

[0170] The measured values for the invention are listed in Table 1below. TABLE 1 Outside the yellow In the yellow Colored VariableDiffuser printed square printed square Total transmission at 500 nm87.2% 90.2% Diffuse transmission at 500 nm 74.7% 11.5% Diffusetransmission efficiency at 85.7% 12.7% 500 nm a* 0.05 0.2 b* 0.1 6.2

[0171] As the data above clearly indicates, the variable diffusioncomplex polymer lenses formed on the surface of a transparent polymerprovides tailored colored variable light diffusion and % transmissionallowing for brighter liquid crystal display devices and productdifferentiation. From the unprinted area of the film to the yellowprinted specular area of the film the percent total transmission changed3.4%, the diffuse transmission changed 84.6%, and the diffusetransmission efficiency changed 85.2%. The a* value increased 0.15 andthe b* value increased 6.1.

[0172] This example could be utilized as a colored variable diffuser foran application where selective areas of a backlit display have a static,colored element. On example of this could be an LCD (ex. cell phone,PDA) where the manufacturer's name or icon would be displayed in adifferent color in the same area of the display at all times when thedevice is on. The LCD would have neutral colored illumination across thedisplay except where the name or icon would be colored specular light soit will be easily seen. This prevents tampering and rebranding the LCDbecause the manufacturer's name is imbedded in the display and can notbe removed without taking the entire device apart and destroying it. Itcan also be used to create backlit displays with unique and customizablecolors and diffusivities. Theses colors can selectively color anddiffuse different parts of the display for example a cell phone with thebattery indicator always being blue and the phone numbers are displayedin red coloring.

[0173] The colored variable diffuser can display text, shapes, andimages in varying amounts of diffusion or specular areas and differentcolors surrounded by diffuse regions. These colored variable diffuserscan be used in displays and as overheads. As overheads the coloredvariable diffuser has added utility. In an unexpected result, when thecolored variable diffuser was placed on an overhead projector, thediffuse areas were dark, and the specular areas were bright and could becolored. This occurred because when the light from the light source inthe overhead projector hit the diffuse areas of the diffuser sheet, thelight was diffused and the focusing lens did not collect the light andthe image projected was dark. The specular areas transmitted specularlight producing bright colored areas on the display. Colored variablediffusion sheets, with there ability to produce colored text, shapes,and images with diffuse and specular areas, can be used as projectmaterials to improve the contrast in the projected sheet allowing thedisplay to be more easily read in a bright room and producing an unusualdisplay effect.

[0174] This colored variable diffusion film example would be utilized ina back lit display to even out the color and illumination of thebacklight across the display. The film would most likely require agradient of diffusion and color, as to not be se by the viewer. Thepercent total light transmission would increase and diffuse lighttransmission would decrease from the center of the roll to the edge ofthe roll. The film would be more diffuse and less transparent in thecenter of the display where the light is located, to compensate for thelight intensity of the light bulb. Towards the edge of the film anddisplay, away from the light source, more light passes through the filmand the light is diffused less to create an even light intensity acrossthe entire display. This tailoring of the diffusion film to the back litdisplay enables a brighter display. The diffuser with tailored of totaland diffuse transmission of the roll across the roll can deliver morelight intensity and more uniform light to the viewer. It has been shownthat selective coloration of the variable diffuser creates an even colortone across the display. For example, a display might have a red tint toit and the desire is to have a neutral display. The diffuser for thelight source would nee to have a cyan component to it, higher in densityclose to the light source and lower in density away from the light tocreate an even color across the display. Using colored variablediffusers displays can be fabricated with even illumination and coloracross the display.

[0175] Further, because the invention materials were constructed on anoriented polyester base, the materials have a higher elastic moduluscompared to cast diffuser sheets. The oriented polymer base of theexample allow for the light diffuser to be thin and therefore costefficient and light as the materials content of the example materials isreduced compared to prior art materials.

[0176] While this example was primarily directed toward the use ofthermoplastic light diffusion materials for LC devices, the materials ofthe invention have value in other diffusion applications such as backlight display, imaging elements containing a diffusion layer, a diffuserfor specular home lighting and privacy screens, imaging media, andgreenhouse light diffusion.

Parts List

[0177]2; Light guide

[0178]4; Lamp Reflector

[0179]6; Reflection tape

[0180]8: Reflection film

[0181]10; Reflection tape

[0182]12; Colored variable light diffusion film

[0183]14; Brightness enhancement film

[0184]16; Polarization film

[0185]18; Visible light source

[0186]20; Transparent polymer base

[0187]22; Major lens

[0188]24; Minor lens

[0189]26; Surface of transparent polymer base

[0190]30; Complex lens

[0191]32; Flattened complex lens

[0192]34; Yellow colorant

What is claimed is:
 1. A light diffuser comprising a macro diffusionefficiency variation wherein at least part of the diffuser is colored.2. The light diffuser of claim 1 wherein said color has a density ofgreater than 0.2.
 3. The light diffuser of claim 1 wherein specularareas of said macro diffusion efficiency variation are colored.
 4. Thelight diffuser of claim 1 wherein diffuse areas of said macro diffusionefficiency variation are colored.
 5. The light diffuser of claim 1wherein gradient areas of said macro diffusion efficiency variation arecolored.
 6. The light diffuser of claim 1 wherein said colored part ofthe diffuser comprises dye based colorants.
 7. The light diffuser ofclaim 1 wherein said colored part of the diffuser comprises pigmentbased colorants.
 8. The light diffuser of claim 1 wherein said coloredpart of the diffuser comprises fluorescent materials.
 9. The lightdiffuser of claim 1 wherein said part of the diffuser corresponds tocolor wavelength band of from 10 to 70 nm.
 10. The light diffuser ofclaim 1 wherein said colored part of the diffuser comprises text. 11.The light diffuser of claim 1 wherein said colored part of the diffusercomprises graphics.
 12. The light diffuser of claim 1 wherein saidcolored part of the diffuser comprise an image.
 13. The light diffuserof claim 1 wherein said part of the diffuser comprises chromatictransmission.
 14. The light diffuser of claim 13 wherein the chromatictransmission comprises yellow light at 570 to 620 nm.
 15. The lightdiffuser of claim 13 wherein the chromatic transmission comprisesmagenta light at 630 to 690 and 425 to 480 nm.
 16. The light diffuser ofclaim 13 wherein the chromatic transmission comprises cyan light at 480to 520 nm.
 17. The light diffuser of claim 13 wherein the chromatictransmission comprises red light at 630 to 690 nm.
 18. The lightdiffuser of claim 13 wherein the chromatic transmission comprises greenlight at 525 to 590 nm.
 19. The light diffuser of claim 13 wherein thechromatic transmission comprises blue light at 425 to 480 nm.
 20. Thelight diffuser of claim 1 wherein the diffusion efficiency varies morethan 5 percent in two different locations of the diffuser.
 21. The lightdiffuser of claim 1 wherein the diffusion efficiency varies more than 50percent in two different locations of the diffuser.
 22. The lightdiffuser of claim 1 wherein the diffusion efficiency variation comprisesa gradient.
 23. The light diffuser of claim 1 that is rectangular inshape wherein there is diffusion efficiency variation along a diagonalof the rectangle.
 24. The light diffuser of claim 1 that is rectangularin shape wherein there is diffusion efficiency variation along the widthor height.
 25. The light diffuser of claim 1 wherein there is diffusionefficiency variation from the center to the perimeter.
 26. The lightdiffuser of claim 1 wherein there is diffusion efficiency variationalong the perimeter.
 27. The light diffuser of claim 1 wherein thediffusion efficiency variation is such that iso-efficiency exhibits anelliptical pattern.
 28. The light diffuser of claim 1 wherein thediffusion efficiency variation comprises a repeating pattern.
 29. Thelight diffuser of claim 1 wherein the diffusion efficiency variationcomprises a specular component.
 30. The light diffuser of claim 1wherein the diffusion efficiency variation provides values is at least10% less on the edges than in the center of said light diffuser.
 31. Thelight diffuser of claim 1 further comprising a base and a plurality ofconvex or concave complex lenses of the surface of said base.
 32. Theplurality of complex lenses of claim 31 wherein the said convex orconcave complex lenses are randomly distributed on the surface of thebase.
 33. The plurality of complex lenses of claim 31 wherein saidconcave or convex complex lenses have an average width in the x and ydirection of 3 to 60 microns.
 34. The plurality of complex lenses ofclaim 31 wherein said concave or convex complex lenses have aheight/diameter ratio of 0.03 to 1.0.
 35. The light diffuser of claim 1further comprising a microvoided polymer sheet.
 36. The light diffuserof claim 35 wherein the microvoided polymer sheet comprisessubstantially circular voids.
 37. The light diffuser of claim 1 whereinsaid light diffuser comprises a surface diffuser.
 38. The light diffuserof claim 1 wherein said light diffuser comprises a bulk diffuser. 39.The light diffuser of claim 1 wherein said light diffuser comprises abase comprising a surface microstructure.
 40. The method of applyingcolor to macro diffusion efficiency variation comprising color transfer.41. The method of claim 40 wherein said application of color transfercomprises inkjet.
 42. The method of claim 40 wherein said application ofcolor transfer comprises electrophotography.
 43. The method of claim 40wherein said application of color transfer comprises flexo, gravure, orscreen ink printing.
 44. The method of claim 40 wherein said applicationof color transfer comprises thermal dye transfer.
 45. A media comprisinga colored part of the diffuser that forms graphics, text, or images. 46.A back lighted imaging media comprising a light source and a lightdiffuser comprising a colored part of the diffuser.
 47. A liquid crystaldevice comprising a light source and a light diffuser comprising acolored part of the diffuser, wherein the light diffuser is locatedbetween the light source and a polarizing film.